Cories like to be in groups - I'd do at least 6, you could do more like 8 though if you want.
African dwarf frogs are cool but not very competitive eaters. So you would need to hand feed (tweezers work) daily to ensure he gets enough. Frogs shouldn't look skinny. In a larger tank this may be difficult to do.
None need live plants. However, something tough and hardy like Java fern should stand up to some picking. I haven't had mollies and plants, but it is worth a try with Java fern.
If you have any female livebearers you will have gradually increasing numbers...