i saw in an old post that removing the passenger footpegs isn't completely neccessary when putting on a highmount pipe, but is it possible for a passenger to still ride? wouldn't they just burn their leg everytime?

depends on the size of the passenger....if they are small and can tuck and wont move they "should" be ok but they def need to watch where their feet are. there really is no room from error....unless you get a carbon pipe...from what i understand carbon fiber really doesnt get hot at all, but im not sure, but if that is the case, then run that and there is more room for error with a passenger on the highmount

Depends on the exhaust. When you go high-mount there are 2 styles, inside and outside.
This refers to the mounting in relation to the bracket.
If you get a can that is "inside", the can can will be between the peg bracket and the fairing. You should have no problem with riding 2-up other than you pass will be warm from the ass down.
If you get a can that is "outside", the can will be ...well it'll be outside of the bracket and generally means jetison of the foot peg itself to accomodate. This would be bad if you intend to bring others.