If you're trying to keep within the "1 inch per gallon" I wouldn't go for corys, they like to be in groups - i.e shoals of 6 or more. And also, "emerald cories" aren't corydoras at all, they're brochis, although they look very similar brochis grow quite a bit bigger, often double the size of your standard cory cat, and the LAST thing I'm guessing you want in a 10 gallon is to be fishing out loads of tiny fry! Someone else might be able to help me here though, in a 10 gallon would a pair of pygmy cories work or would they want the security of a bigger group?
Dalmation mollies can and do grow quite big, 3 inches sounds about right. A decent centrepiece IMO is a single male dwarf gourami or a betta - about 2 inches maximum in size for both. Mollies can become slightly aggressive, males especially, but I'm not sure whether this is only because of mating competition, I've never kept them singly. If you want a molly though make sure you buy a male rather than a female who is likely to be already pregnant. And also, the reason you won't specifically find a page on "dalmation mollies" is because these are just a variation - they're part of the species
Poecilia sphenops which includes sailfin mollies, silver mollies, black mollies, lyretails etc etc.
It sounds like you're putting a lot of thought into this which is really promising and should result in a very rewarding hobby