In a small city of about 10,000 people- how big should the thieves' guild be?
Relevant information- there is only one thieves' guild in town, they've worked pretty hard to run any competition into the ground- and participating in a non-guild job is a very risky. The Thieves' guild is pretty well-integrated into reputable businesses, so the line between cutthroat business tactics and just cutting throats is pretty thin. They also control two seats on the 7-seat town council.
The town isn't lawless by any stretch, it has your typical town guard contingency and maintains its own (albeit small) military force. The Thieves' guild is simply good at bribing, hiding, and extorting.
For those of you who have it, I'm using the Restenford thieves' guild affiliation from PHBII if that matters. It's also a 3.5 campaign.
I want this to be a force to be reckoned with, but I want this to be realistic too. A guild too large (or too small) wouldn't make sense, so I'm searching for that perfect number. if you can give it to me, perhaps you could also help with the distribution of forces? Assuming the leader (and most powerful member) is about CR 12, how does the breakdown happen from there? (i.e. how many first, second, third lvl NPCs, of what general classes, etc.)
Any help is appreciated! Thanks!