IMO, it all depends on what type of driving/offroading you will be doing. after i installed the 4.5" lift and 32x11.50's, i thought i was good to go. as far as bumpstops, the only ones i installed were the front bumpstops that came with the RE lift. and none in the rear. i had pleanty of room for around the town driving.
but once i went offroad and disconnected my swaybars, that all changed. i had to remove my flares to even before i tried to flex.
here are some pics i've taken in the past to help answer these questions ...
all pics linked to kelp 56k'ers
for reference, here's how far the 32x11.50's stick out when mounted on 15x8 rims with 4" of bs'ing...
with flares...
http://viewsfrommylens.com/Gallery/albums/album12/PICT4100.jpg
w/out flares...
http://viewsfrommylens.com/Gallery/albums/album12/PICT4466.jpg
first offroad trip...
no bumpstops in rear and rear not completely flexed out. almost no room left...
http://viewsfrommylens.com/Gallery/albums/album01/PICT4621.jpg
front fully flexed out...
http://viewsfrommylens.com/Gallery/albums/album01/PICT4607.jpg
if i had turned the wheel in the slightest, i would have bent up my fenders
so i broke out the hockey puckes and added bumpstop to the front and that helped out tons...
http://viewsfrommylens.com/Gallery/albums/album09/IMG_0160.jpg
...but left the rear alone...
http://viewsfrommylens.com/Gallery/albums/album09/IMG_0161.jpg
that wasn't a good idea...
http://viewsfrommylens.com/Gallery/albums/album37/PICT6571.jpg
http://viewsfrommylens.com/Gallery/albums/album37/PICT6574.jpg
http://viewsfrommylens.com/Gallery/albums/album37/PICT6572.jpg
so i got out the metal tools and trimmed the fenders front and rear and relocated the flares up to make the va 5-oh happy. now i have ZERO rubbing with running a little bumpstop up front and trimming front and rear...
http://viewsfrommylens.com/Gallery/albums/album44/IMG_3008.jpg
http://viewsfrommylens.com/Gallery/albums/album44/IMG_3027.jpg
i have a set of dpg rear bumpstop plates that will be going in when i go up to 33's with this lift/setup.
hope my experiences/pictures help you out.