I've been looking into getting some thicker strings (.013) and I've been reading that my guitar needs to be setup in order to handle the thicker gauge - but I've also read that it doesn't need to be setup. Whats the deal? Should I get it setup or not?
yes, you should get your guitar set up everytime you change the gauge of string you're using. If you don't, there is a distinct possibility that your neck will warp, besides your intonation being way off.
If you’re going up from .09 or .010 to .013 you’ll need to have work done on the nut, which requires nut files and experience, so have a setup done.