All I can suggest is that you plan ahead on the order you stock them (Sohal shoud go in last, IMO) and research the butterflies you're getting. Some are greedy feeders, some will starve rather than eat anything but live coral polyps. I've kept Forcipger flavissimus and they're very hardy, if a little passive. They will accept virtually any frozen or flake food small enough to fit in their mouth.
P. imperator is one of the hardier large angels, and a good selection. It's diet (like all large angels) should include sponge based foods like "Angel Formula" from Ocean Nutrition. They should also have some type of algae to constantly graze on. OK, so it's not the same exact fish but I feed my P. navarchus Angel Formula, broccoli, fresh shrimp, fresh squid, and a wee bit of beef. He's been with me 2 years come September and is fat and gorgeous.
Can't comment on the diet of the Sohal, I've never kept one. I just know they're mean as hell.
Water conditions should be of excellent quality for all these fish. Ammonia, nitrite, zero obviously. They can a handle a bit more nitrate than corals, but you should strive to keep it as low as possible to reduce algae anyway. All these fish will do much better in a live rock tank as it offers constant grazing of algae, copepods, sponges, etc.
HTH, Matt