about 8-10 and yes you could..other species of small similar tetra (eg. glowlight or rummy nose etc) or zebra danios or platys/guppys or some catfish.
just about anything that will fit into it really!!
Danios? rummy nose? Naaa not in a 10g, most people would say thats even too small for active neons ...If you really want them, id go with somthing closer to andy's idea, cept maybe 6-8 neons.
Well people do keep danios in a 10 gallon but I agree it probably is small for them.
Rummy nose tetras are only around as active as neons and so I don't see the problem