These are my rules for my current attempt at a BACC. These are subject to change (and probably will!!) And I will try to keep these updated as I change stuff.

Starting Out
You must create a new neighborhood. It can be any template, but you may not add a University, Downtown, Shopping District, or any Community Lots. Vacation destinations are allowed. 

 Create a single sim to be your founder. To make it as random as possible, roll for everything:

1-3: male
4-6: female

1: Pleasure
2: Romance
3: Knowledge
4: Family
5: Popularity
6: Fortune

1-3: Column A
4-6: Column B

Column A:
1: Aquarius
2: Pisces
3: Aries
4: Taurus
5: Gemini
6: Cancer

Column B:
1: Leo
2: Virgo
3: Libra
4: Scorpio
5: Sagittarius
6: Capricorn

1-2: Your Sim's a creature! Move on to the next roll to determine what they are.
3-6: Your Sim's just the regular house and garden variety.

1: Zombie
2: Vampire
3: Werewolf
4: Alien
5: Witch
6: Plantsim

As your neighborhood expands, you must play every household for the same amount of time. If you move in townies just for their money and move them back out, they cannot just sit in the Sim Bin. All Sims must be played.

At the beginning ALL careers are locked, meaning no job for your founder. You must find other ways to make money (painting, novels, business, treasure hunting, etc).

Sims may not have fire detectors or burglar alarms until the first position in the Law Enforcement Career is unlocked.

Sims may not call for any services except for the Nanny and Adoption. Service calls are unlocked when the population reaches 500. Pizza and Chinese Food delivery are unlocked with a population of 3,000.

Servos are allowed and do count in the population. Pets are allowed but do NOT count in the population. 

Sims may not sell anything in their community lots that they did not craft/grow themselves until a Downtown has been added.

 

Figuring out Population
Take the SM and multiple it by the number of playable sims. The SM starts out at 1. You add to the SM by adding community lots and unlockables (Business District, University, and Downtown).

+1 for first community lot
+1 at 5 community lots
+1 every additional 5 community lots
+5 for a downtown
+5 for each business district
+5 for a university

 

Unlocking Neighborhood Additions
Community Lot
Buy a community lot or have 4 households. Gives one CAS sim.

Business Districts
Have 10 Businesses (of any rank) and one Business Tycoon. Gives 5 CAS sims.

University
Once a sim reaches the top of the political career, you may add a university. The tuition is §10,000 per semester (§20,000 per year) and scholarships count towards that. The rest of the money MUST come out of the family funds. (No using the familyfunds, kaching, or motherlode cheats). The university is open to anyone, as long as they can pay the tuition. Teens must also have at least 20 skill points in total and have an A in school (private or public school). Gives 5 CAS sims.

Downtown
Have 10 Clubs. Gives 20 CAS sims.

Service Calls
At population 500, service calls (besides nanny and adoption) are available. Food delivery is unlocked at population 3,000. Fire alarms and burglar alarms can be placed when the first position in Law Enforcement is filled.> 

Private School
Private School is not unlocked until a sim has reached the top of the Education career and there is a University.

 

Unlocking Community Lots
A new community lot may be bought by a sim or placed after earning four households. Sims are only allowed to purchase one of the following community lot after they meet one of the following requirements:

Book Store
Sim has written at least 5 books

Bakery
Sim has reached at least level 5 in cooking

Restaurant
Sim has reached at least level 8 in cooking

Toy Shop
Sim has gold badge in toy making

Flower Shop
Sim has gold badge in flower arranging

Clothing Shop
Sim has gold badge in sewing

Pottery Shop
Sim has gold badge in pottery

Pet Store
Family has one pet which learned all commands

Any other community lot is available at any time, as long as a sim can afford it or there is a free community lot available.

Unlocking Careers
Adventure
To open a position in the Adventure Career, a community lot must be placed to represent a Museum. When a playable Sim reaches the top of the career, it is then unlocked to everyone. 

Architecture
A position in Architecture will be opened for every 10 lots, residential or community, and each neighborhood addition (University, Downtown, Business District). The residential lots must be occupied. The community lots must be complete and functional (no blank lots), and can be player owned. Apartments only count as one lot, no matter how many playable families live in the building. 

Artist
The career is open for any Sim who has sold 5 Masterpieces or has a degree in Art. 

Athletic
The Athletic Career path is unlocked as soon as a sports themed community lot is placed. The actual “sport” being played can be anything.

Business
A new position opens in the Business Career track every time a player owned business reaches level 10(home or community lot). When a playable Sim reaches the top of the career, it is then unlocked to everyone. 

Criminal:
Wherever there are people there is also crime. When the population of the town reaches 100 one spot on the Criminal Career track opens. Every time a Sim reaches the top of the Criminal Career, they open an additional position in both the Criminal and the Law Enforcement careers. The Criminal Career track is never truly unlocked, but can have many open positions.

Culinary
The Culinary Career earns an open position for each player owned restaurant business that reaches level 5. When a playable Sim reaches the top of the career, it is then unlocked to everyone. 

Dance
A position in the Dance Career is opened whenever a Sim owned dance studio opens and reaches Rank 5.When a playable Sim reaches the top of the career, it is unlocked to everyone. 

Education
As soon as the 10th child reaches childhood, the town votes they need a school. Now the kids won't need to ride the bus for an hour to the nearest school. Obviously this school needs a teacher, so one spot in the educational career opens up. After that, a new position opens with every fifth child to childhood opens up a new spot. This career is always open to any Sim who has a diploma regardless of population. 

Entertainment
A position is opened whenever a Sim transitions into adulthood with maximum charisma. A position is also available for any sim who graduates with a degree in drama.  

Gamer
For a Sim to become a Gamer they must own all of the following items either in their inventory, the lot they live on, or a community lot that they own the deed to: the expensive computer, video game console, a pinball machine, and an arcade game.  

Intelligence
The career is unlocked once the top of the Law Enforcement and Military career have been reached, but is only open to Sims who graduated college with a GPA of 4.0.  

Journalism
When the town reaches a population of 1,000 the first position in Journalism is unlocked. An additional spot is added every 1,000 in population thereafter. Every time someone reaches the top of the Law Enforcement, Criminal, or Show Business career tracks an additional position can be added.  

Law
A position opens up every time a Sim gets furious at someone. To enter the career this way, a Sim needs to have studied Couples Counseling. The career is unlocked for everyone with a University degree in Political Science as long as one sim in town is furious at another sim.

Law Enforcement
After three fires and/or burglaries or after a sim reaches the top of the Criminal Career, one position is unlocked. This career is never truly unlocked

Medical
When one of your Sims has fallen ill, and has passed on their disease to at least 2 other sims, a position opens to one Sim who has studied Physiology. When a playable sim reaches the top of the career, it is unlocked to everyone. Any sim who graduates from University with a degree in Biology can get a job regardless of if the career is unlocked or not.

Military
The Military Career track is unlocked when a community lot is placed that represents a military base. It takes the place of a NPC community lot that you can add once you accumulate 4 households, but it does not contribute to the total number of community lots present and can never be purchased by a playable Sim.

Music
The Music Career is unlocked when a music venue community lot is placed. To be considered a music venue there must be a stage and at least 3 music instruments. This lot can serve other purposes other than just music, such as a park or club (won’t count for the slacker career).  

Natural Science
The career is open for any Sim with a golden gardening talent badge or a University degree in Biology.  

Oceanography
The career is open to any Sim with a golden fishing talent badge. Once the first Sim reaches the top of the career, it is unlocked for everyone with a degree in Biology.  

Paranormal
A position opens when the town builds a cemetery and 5 graves have been sent to it. 

Politics
Once the town has 5 households, the need arises four a neighborhood counsel. Since every household has a veto, not much gets decided. So after 5 meetings, the households decide they need a leader. This means one week after the town reaches 5 households, one spot in the political career opens up. Once that sim reaches the top, the career is unlocked for everyone. But there can be only one Mayor at any given time.

Science
A Science Career position will be earned every time any Sim transitions into Adulthood with maxed Logic. A position can also be opened for every 3 electrocutions by electronics or lightening. When a playable Sim graduates from a university, the career is unlocked to everyone.

Show Business
A position is open for every Prestidigitator (entertainment) and Professional Party Guest. Whenever a Sim reaches the top of the career, a position is opened in Journalism after the population reaches 1,000. 

Slacker
A position in the Slacker Career is opened every time a community lot is created for the soul purpose of being a “Club”. It is unlocked completely when a Downtown Area is Unlocked.

Pet Careers
Show Biz
Only pets who have learned all commands (excluding toilet training for cats) may enter this career.

Service
 The career opens once phone service options are unlocked (when the population reaches 500).

Security
 Only pets whose owner works in Law Enforcement may enter this career. 

 

Apartments
Each family living in an apartment counts as a separate household when calculation how many free community lots you can have. However, each apartment building counts as one lot towards the Architecture career.

You may not ask the landlord to do repairs or other chores until service calls are unlocked (population 500). The landlord doing his daily rounds is okay.


EDIT:
Once a sim has become a City Council Member (level 5 of politics) they want to start raising funds to better the community. At this point a weekly tax of 5% of the lot value will be sent to the Council member. The funds will be used to buy community lots (parks or other "community" places) and build career buildings (school, police department, etc.)