I don't know if adding more angels is a good idea, especially if any of them pair up. Territoriality can cause a lot of problems in your tank. The one inch per gallon rule is a rule of thumb that allows easy calculation, and must be applied in conjunction with common sense. 10 neon yellow rasboras in a 10 gallon tank? Sure. 10 neon tetras in a 10 gallon tank? Sure. 10 neon yellow rasboras *and* 10 neon tetras? Probably. 1 pictus catfish? No, because at full growth of 8 inches, it'd have a hard time turning around.