Good question.  The Protev has a crew complement of 500, so it couldn't be any more than that.

If we presume the Arcova's crew (75) is the bare minimum to operate the craft, then 425 represents the "colonizing" crew.  Colonizing requires 90 antimatter, and total antimatter capacity is 225, so my best guess is 90*425/225 = 170 people.

I'm presuming this is just the initial force, and additional forces would arrive shortly afterwards (this would be abstract, in the same way that the game references ship supply chains that don't appear in-game.  We just hand-wave it and pretend it's happening in the background).

True, I was using TEC as a baseline, but I'm more or less making a guess on the subject anyways.  The Vasari number is largely irrelevant since the manual indicates all Vasari ships carry an unspecified number of civilians in addition to military personnel.  So really we're just comparing the Advent and TEC varieties.

The implication I get from the game is that ground combat is essentially super-charged version of trench warfare where the defender always wins, and the only way to get a foothold is to blast them out with orbital bombardment.