Hi Moose,
'mainland reef led light'... is that perhaps 'marineland' led? The intensity and color of your lighting is of supreme importance when keeping corals. If it says 'reef' light, you're probably good for soft coral, zoanthids, mushrooms, etc... but I'd need more lighting details in order to recommend any of the more light loving corals. Nothing wrong with soft corals, that's where I started, mushrooms, leathers, colt coral, xenia... it can be quite attractive, and is probably fine under your lighting.
You didn't mention substrate, do you have a sand bed? Crushed coral? Bare glass? It makes a difference... 1 lump of live rock, unless it's a 50lb lump, is probably insufficient surface area for a healthy biological filter. The 20lbs you're adding will help dramatically, but it's still a little light... most folks recommend somewhere between 1 and 2 pounds of rock per gallon of water. With a good sand bed, that can be reduced a little, but the more limited your bio filter is, the fewer animals you're going to be able to support. I'd look at another 50 lbs of live rock... or even dry base rock, which will grow into perfectly acceptable bio filter habitat, given a little time.
The fact that you've lost 2 coral beauty angles and a yellow tang is concerning... 1st, depending on the size of the fishes, 2 tangs, 3 angels, and a pair of clowns is a pretty full 55g tank, especially with limited bio filter habitat. You might check and post your ammonia, nitrate, and nitrite readings. Don't overload the tank's capacity to process waste materials... and my one key piece of advice... MOVE SLOW. Picking up a half dozen fish and dumping them in at once is generally a bad idea, especially in a fairly small, or fairly new, aquarium.