Seranov |
Yes, you can be a Phalanx Fighter (Fighter) at 1st level, take a level of Acrobat (Rogue) at 2nd level, and then take a level of Martial Artist (Monk) at 3rd. You can stack as many archetypes as you like (so long as they don't ALTER or REPLACE any of the same abilities).
But it'd be a really bad idea, so I'd advise against it.
Starglim |
1. Taking archetypes for different classes should pose no problem. They don't really stack or interact. It's just that the same character happens to have them.
Note that with three levels in three different classes, you've built a martial character with a +1 BAB at third level (good thing he started as a fighter, otherwise it would have been +0 at second level). His saves and class skills might look better.
2. PFS uses strictly the published rules unless something is stated as an exception. In the case of archetypes, you're allowed to take an archetype at a higher level as long as you haven't received any of the abilities that it modifies, though that doesn't affect the present question. All three of these archetypes are legal for play.