I've always heard that you should have 10g of water per angel. I have 2 in my 55g, and I keep them with black skirt tetra's, Columbian tetras, Jumbo neons, danios, and a dwarf gourami. If you have good filtration and do bi-weekly or weekly waterchanges, you could get by with adding a small school of small tetras, or a couple of 2-3 inch fish. If you add the smaller fish now, the Angels won't likely to see them as food when they get bigger.
SKEL