I have a copaxi solarion who just reached 8th level in Society. They've been a lot of fun, but some of the biggest struggles/challenges have included:
* With Cha and Str being so important to the class (esp. a solar weapon build), Dex got a bit shortchanged. Taking Heavy Armor Proficiency at 1st level helped, but they still get hit a lot. Boosting Dex at 5th level and as their second personal upgrade made a HUGE difference. But Voran also has a charge schtick in their build, so I think I need to bite the bullet and take Improved Initiative so they can do that earlier in the fight.
* Skill Adept is difficult to exploit fully due to limited skill points, and the class is unlikely to prioritize Int. Both of Voran's choices were trained-only Int skills (Culture, Life Science) so that they could make checks on stuff that comes up often in Society play. I've only able to afford to keep one at max ranks, though (Culture, to get full use out of the copaxi's natural communicator trait).