IME, Mollies are high waste producers, and far too large and too good of swimmers to go in anything less than a three foot tank. My mollies averaged 3-4" and swam they entirety of my 55g.
Pygmy corydoras would be suitable for a 10g, but again, 10g just doesn't provide the swim space that regular corydoras need. They can also be difficult to find in lfs, but are more easily purchased online.
A betta with a mystery snail and some shrimp would be great for the 10g.
Ember tetras and Yunannilus cruciatus (which are a type of loach) are a good size for a 10g tank and like the warmer temps that bettas need. Both prefer schools, though. Unless you've got a good local fish store in your area, you may have to purchase them online. Both require stable water parameters, so a thoroughly cycled tank would be good to have first.
Pygmy corydoras are another great option.
A few otocinclus are another possibility if the tank is stable and cycled.
Horned nerites are really cool looking and have a smaller bioload than mystery snails.
There really are a lot of options if you're able to purchase online or have a pet store that can order fish for you. (Also, I wouldn't recommend all of those fish in one ten gallon; those are just some of the possibilities.)
I have 2 panda cories and 2 Venezuelan Sailfin cories (variation of bronze cory) in my 10g. Actually cories are relatively stationary fish and don't move a whole lot (unlike say, danios) so a 10g provides enough space for most of the cories available in the hobby. 99.9% of the cories in the hobby don't get over 3" long. 3-4 cories and 3 platies would work in a cycled, mature 10g with a good filter.
Haha, it's not that mine don't move. They do, they scuttle here and there all day. But as far as needing lots of space to swim rapidly, like neons or danios, I don't think cories qualify. Where neons and danios swim all day, cories . . . explore, is the word I'm looking for. They're very curious fish and will explore every inch of your tank but they don't need to be on the constant move.
Ah, but in the end, it's up to the aquarist to make the call. HB, it's up to you to decide if 10g is enough for cories or not. Good luck.
I have 2 panda cories and 2 Venezuelan Sailfin cories (variation of bronze cory) in my 10g. Actually cories are relatively stationary fish and don't move a whole lot (unlike say, danios) so a 10g provides enough space for most of the cories available in the hobby. 99.9% of the cories in the hobby don't get over 3" long. 3-4 cories and 3 platies would work in a cycled, mature 10g with a good filter.
I've heard before that platies are a bad match, due to their color. Any truth to this?
Also, is there any easy way to tell ahead of time of my betta will respond well to other fish? I was going to let the other fish in the tank first, then put the betta in a small bowl and let it float to see if he seems especially agitated. Are there better ways of checking?