1. Can't speak for attributes but for abilities it's 5. Apparently you can raise it above this with gear though, but not points.
2. No, it's for that character ONLY. Make sure to use him/her to open chests and such! Same for barter, instigate the conversation with the person having barter, and your whole team benefits (not quite sure that's intended, but that's the current system).
As for Perception, yes, again one person, however if moving in close proximity it doesn't matter that much. However it would affect if you start splitting your party (especially with mines, which need perception to spot. Sending a scout out infront with low perception may lead to trigger them)
3. Can't say, haven't gotten that far myself yet XD
GO FOR THE EYES BOO!
* I'm pretty sure it's here... but they read both. If Steam forums I visit are any indication though, you're less likely to drown in the posts here or get flamed on etc.