DOnt know the sizes of angels but it is lot for 75G. But as long as you are top of it, why not?
Adding more fish to it, I dont know?
Provided that angels are very small to mid, festivum or gbr or other small bottom dwelling dwarf cichlids would be nice. Could look into Geophagus Species also!
You could add one or a pair of my oblongum's w/out any worries (aside from overstocking.) They're mellow enough to mix with curviceps or festiviums, really can't imagine conflict with angels. The small cherry barbs may eventually become food, I'm not sure how large they grow. The ones I have available are 2" or less, and will take at least until the end of next summer to reach full adult size. Males max out at about 5", females 3".
UI have blues in with wild angels and it is comical to watch as the rams have 0 fear of the angels and will dart out and take food from them.
the angels will give chase but the rams are much too fast.
also Keyholes work well , tho not as colorful. they are entertaining. mine would make piles out of the gravel.
I am looking for more keyholes now