It's never too late to add live rock. I am constantly, slowly adding rocks to my tanks just to keep the credit card bill down, lol.
I'd put the tang and angel plan on hold for a while. At least until you get a bigger tank.
If you really want an angel try the dwarf angels. They don't get nearly as big. Maybe a flame angel or something real colorful. Most of us are cursed since the nicest, most colorful angels are never reef safe. Since you don't have coral, I'd say go for it. Since you don't have any LR
in the tank right now, you may experience another cycle, so look for cured live rock and add slowly. If you can have someone hold on to your damsels, it would make this much easier. If anything get rid of them because they get to be real buttholes... They look nice until they start going after $100 triggers three times their size, IME.