If it's got Vasari colony pods, quite a lot (but perhaps in cramped conditions- say that the Spartan-like Vasari don't seem to mind). If without colony pods, the Vasari should have the least number of people- in fact, it wouldn't be bad if you could have only a few dozen personnel, all wired up and connected to the various starbase systems, mostly organising and giving orders, with automation and nanobots doing most of the work.
TEC should have quite a lot of personnel, with many involved in trade ports and construction bays. There should also be a lot of non-military personnel too, with all the trade going on- think Deep Space Nine.
The Advent should be somewhere in the middle- think of their Starbase as a huge cathedral, not filled with people, but still able to contain quite a few. There should of course be more specialization and unity (heh) among the personnel, compared to a TEC starbase. And it would certainly be much more quiet.