Another plant that can attach to things is anubias. There are a bunch of varieties and all should work. I have a tank with four different types
There are other mosses you could try, I'm a fan of flame moss.
As for floating plants, try water sprite. It can live when planted in substrate but does just as well floating. It'll appreciate the new lighting and grow quickly. Duckweed is another good floating plant but it can be a nuisance to some people since it grows so fast and is annoying to remove.
For other shrimp, check out cherry shrimp and amano shrimp. Those are my favorites. Cherry shrimp are pretty and breed like crazy. Amano shrimp are larger and unlikely to breed but they're neat...mine always ate out of my hand.
For a snail, it sounds like you'd want a freshwater nerite snail. They're hardy, eat algae, won't bother plants, and won't breed in freshwater. What temperature is your tank?
The ACFs I've known would have eaten White Cloud Minnows. If you don't think your frog will, go for it. Even "large" ones are pretty tiny, though! I love them...they're hardy, pretty, and active. They're fast enough to swim away from a hungry frog but it would be stressful if they were constantly chased. If Squishy is a lazy hunter it should be OK. I'd get at least six, they're schooling fish