Here are some thoughts on your stock list. First off, pass on the tang. A scopas gets as big as a dinner plate and has no place in a 55g tank.
Secondly, wait on the mandarin for some time. There wont be enough pods
or food in the tank if its new for quite a while. getting an ORA mandarin is also another thing I would suggest when its time to get one as they have a better chance of eating prepared foods.
And finally, 2 pairs of clowns in a 55g will kill each other eventually. i had two pairs in my 6 foot tank and after about 3 months of being happy together the one pair went blood crazy on the other pair and I had to remove a pair or face them dying. I happened to have a place to put them so it worked out but most people dont have multiple tanks.
Everything else looks good. There are plenty of options for fish so dont worry about not having the tang, you can get a cool fish that is appropriate for your tank withotu much effort.