6 neon tetras + 1 beta + 6 cardinal tetras + 1 to 2 snail OR; 2 platys + 6 guppies + 6 panda cories + 8 ghost shrimps + 1 snail. Whether it is a 5-gallon, 10-gallon, 20-gallon tank or even the bigger ones, providing safe and healthy environment is the key to keeping any kind of fishes including tetras. read more
With 4 platies you have pretty much maxed out a 10 gallon tank. If you really want to add a few more fish you should upgrade to a filter for 20+ gallons FIRST and then add 4-6 neon tetras. Neons will have the least impact on your bioload and they need a shoal of 4-6 to thrive. read more