Too deep really for an ADF and also too many tank mates. Please read up on their care.
Is your water soft and acidic or hard and alkaline? Neons and DG in the former, livebearers in the latter.
Cories prefer soft but can adapt to hard if water parameters are very good. They should be in a minimum shoal of 6, so I'd encourage you to look at smaller ones, such as pandas in order to fit in a 20 high.
As for neon tetras and DGs, find out how likely they are to survive. Around here, neon tetras and DGs come from Thailand, and very few of them survive the trip. Once here, the survivors are exhausted and often go belly up. They also get bred with a lot of antibiotics in Thailand, and have some very drug-resistant diseases. I've sworn off of them after losing way too many.
If your water is hard and alkaline, I'd recommend sticking with guppies as they swim all over the tank, are colorful, and their antics are hilarious. Endlers, of course, are my favorite, but I know that people like those monster ballgowns that the fancy ones have instead of tails.