Should be a fine route. It's one of my favorite areas of the park. Cliffs, pictographs, waterfalls... it has it all.
I can't tell you much about campsites on Lerome itself. Presumably you understand you'd be on "Crown Land" (I think) but certainly NOT in Quetico itself so, if you camp outside of the park, you'll need to secure appropriate authorization.
Depending upon how muddy the portages are, it should take you just shy of five hours to get down to the Sue Falls area, where you can use your park permit to camp. The portages are pretty simple, though the last one is longer & a lot of uphill IF you are returning (ie. "exiting the park") in this direction. Since the serious blowdown a few years back, some of the better campsites around the falls aren't what they once were but most are serviceable.
If your loop is Cirrus to Quetico to Oriana you'll find plenty of fine campsites along the way that are clearly marked on most park maps. You didn't mention where you would exit. However, if your loop takes you back out via Lerome, exercise some caution before considering the long-ish portage from Kasakokwog back to Cirrus. It can be tricky when wet, given all the up-and-down on slippery, gravelly surfaces.
Fishing should be good for all 4 major species throughout your route.
There are others on this board who may be able to help you with campsites "outside" of the park (such as on Lerome). As for me, I never considered a Crown Land permit and I always just bee-lined it down to Sue Falls.
Good luck!
Jimbo