I plan to switch from a sps,lps,softy mixed reef to a ric/zoa tank with a few LPS. I'm sure you won't have a problem, but I would guess the tank will change appearance from time to time as some zoas and Rics overrun one another. Keeping them separate on different "islands" will probably help you maintain your diversity. My first tanks were softy tanks that were very easy to maintain using just water changes. I'm tired of all the additions. It's pricey and I have to test my water all the time which is even more cash. I'm looking to go back to the easy life and I'm selling off my sps now. Those are pretty big fish in that system and I expect they will create a lot of waste which shouldn't be a major problem in a softy tank. The tang will eventually have to move into a bigger tank as the years go on. You will have more than enough light for that set up, and I have found my 36in 6x39w bulbs over my 48in 75 is good for my sps, but my lower light corals suffer. You might want to use extra actinic bulbs that don't put out too much par or keep your lights high to acclimate the lower light corals.