gollus, lnb is one of my fav but sometimes they nip on corals and clams
you can try copperband they are safer but harder. There are more reef safe butterflies.
i wouldnt mix two dwarf angels because they can chase each other expecially lemonpeel is one of the most aggressive dwarf angel but i believe you mix two, three or more of the same species. If two they will pair up if three or more they will school, that what i heard but dont have any experience... In Turkey there are people keeping two same kind dwarf angels like flames and they all swim everywhere together. They also lay eggs if i remember correct.
For tangs, i would just add one, not common tang. Sure as jwtrojan44 said you have loads of rocks so i wouldnt add a big tang like sailfin, naso or unicorn. What about hippo, clown, powder blue, achilles, white cheek or as waterfaller said black zebrasoma tang? Except hippo and black tang these are very hard fish but i love both hard and uncommon fish. Also having a healthy, well GROWING hippo tang is rare these days...
Good Luck