Re fish limitations: they grow. Remember we're talking about reefs, and the example given is a 55, which shouldn't have tangs, and angels (even the recommended ones) can take after your corals. Go to a 120, and you can manage a wider range of species. But just yesterday, talking to my lfs owner, she'd had a rabbit that had been in a 120 about 3 years suddenly decide coral was on the menu. Rabbits are essentially vegetarians. They aren't even supposed to like corals. Surprise. The damage was several hundred dollars worth. One supposes he just got bored. Angels in a reef? Even after a year or so, they're notorious for changing their mind and taking after corals. If a reef is your aim, you're going to have quite a large investment in corals, even if you grew it---and trying to extract a fish from a well-grown reef is not easy.
Re the inverts, I have plenty of crustaceans and snails and inverts of all sorts. I just avoid certain ones, listed above, that kill things you generally want, like fish, or that cause problems. The notion that an emerald crab is going to eat all your bubble algae is kind of urban legend: the facts are, not that much. I think one I had ate about 3 bubbles and half my mandy's tail, though it grew back: emeralds are a case of "If you want it, have it, but don't expect it to really do that much for your tank." They're cute, they're personable, and if you like them, great. URchins are in the same category. I won't, however, recommend the sally lightfoot, which grows large (as a dinnerplate) and begins to go after your fish. The emerald mithrax stays small, as do good micro-hermits. I prefer the scarlet hermits in general, and always have a handful, though my current favorite is a striped fellow whose main claw is just a little too large for my liking, though I've never caught him doing damage. Re the pistol---I had to nearly unbuild a reef to catch mine, which was doing in fish at a fair clip: I pass you my experience, tiger pistol and yellow watchman: he killed the watchman, then went serial killer on me. Why, whether it was gender, maturity, etc, I have no idea.
Re the flow, I can't give you a precise flow, but in my 105 I have a 2000 gph throttled back to about 1000-1250, because it will generate too much splash coming in, plus I have two strong powerheads at low level (it's a very deep tank, and I need to both agitate the surface (one powerhead) and the depths (the other blows through the lower rock caves.)