I don't keep sharks, but I think as you research and get more input, you'll find that a 125 is not recommended for any adult sharks.
Clean up crew totally depends on what fish you have in the tank. Many predators will eat hermit crabs and snails, some will leave them alone. Urchins, sea cucumbers and brittle/serpent stars are other cleaners to consider, and will be safe with some predators.
In that sized tank, IMO, you could keep several fish from this list (but not all these are compatible, you'd need to check once you get your stock list started)
-smaller triggers (up to 12") - e.g., just about any Rhinecanthus, blue throat - some smaller triggers are too aggressive for a community (i.e., undulated)
-moderated sized puffers - like dogface or spiny box puffer
-moderate sized eels - like zebra moray, snowflake and relatives, some of the smaller and mellower (2-2.5 foot) piscivorous eels. There is a great chapter in Reef Fishes volume 1 and good info on wetwebmedia on suitable eels.
-smaller tangs - yellow, mimic, kole, etc. - stay away from really large, delicate or aggressive tangs (e.g., NO to Sohal, Naso, achilles)
-dwarf and medium angels - some get good size on them - for example, Centropyge heraldii can get to 8 inches. Some of the Genicanthus are under 10 inches and can be paired.
-some lionfish (dwarf or medium better than larger, like Volitan)
-moderate sized wrasses - one of the best, IMO is Australian Harlequin tuskfish - some are aggressive and/or need a sand bed to bury in. There are a lot of great wrasses to choose from. Most will eat hermit crabs and may bother snails.
Many (or most) predators produce a lot of waste. I'd be sure to invest in the best protein skimmer you fit/afford.
Hope this helps. 125 is a nice size and length. I'm finding that no tank is really big enough for all the fish I'd like to keep.
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