theres nothing that special i've done, and i had a thread but was lost in one of the site crashes years ago
and there is a tonne of room in 17's to fit 4pots, check http://www.clubsub.org.nz/forum/index.php/topic,29823.msg409797.html#msg409797 for pics of my current 4pots (294mm disc) in 17" rims, I'm going to brembos and they have a way bigger disc and they will still fit. as it's been said before, it's all about offset AND spoke design. only sure way to know if they're gonna fit is to try them.
and as for rolling guards, i run 215's on single spoke rims, I've had the car so low i couldn't turn the steering wheel cause it rubbed on the inside of the wheel arch, never had an issue with the outer guard rubbing so don't think you'd need to roll guards, i think forester guards are quite big to accommodate for "offroading"