The clowns should be fine. A 120g has plenty of space to avoid nipping issues especially as the OP is keeping them in a large group, better than anyone else who buy less than five.
Either kuhlis or clowns will work. You won't have problems with clowns however considering your tank size but if you prefer kuhlis, go for it. You won't have to upgrade the tank after 4 years of having the clowns. Lemons, pristellas, hatchets, beacons, diamonds, columbians, phantoms and bleeding heart tetras work with angels.