What do you think about Watersprite in the back left corner? Maybe even some sort of carpeting?
Sure :) As your tank is lowlight You can try carpeting with moss on mesh. dwarf sags could also work, but depending on the type you get some can get to 7in or so. marsilea species are also great but grow slow. some of the low lying crypts also do great for a foreground plant, you can also try microsword and pygmy chain sword :)
I don't think I want to add anymore fish in there.
OK =D that works too :)
I was thinking along the lines of more invertebrates or maybe a frog?
I'm not very familiar with frogs, but I believe for some, the water can't be too deep >.<
As for other inverts, the amano shrimp is very loveable, and at a good sized shrimp so your betta won't eat it =D
Also nerite have fascinating shell patterns and can make a great addition to the tank.
I would probably avoid bamboo shrimps since they are filter feeders and harder to keep alive
In total, I'll have 1 Betta, 1 Nerite snail, 2 Ghost shrimp, and soon to be 3 Blue Mystery snails.
Sounds good :)
If I have that all together, how many more shrimps can I handle?
what kind of shrimp do you want to get? you can probably have 30 ghost shrimps in a properly cared for 10 gallon XD
Also, is a Dwarf Frog even an option with all that other bioload?
Your bioload is OK for now. I heard frogs are messy eaters, feeding the frog may also be a problem since the betta may be inclined to steal his food.