Hello and welcome to AA!
Dwarf frogs are social critters and should be kept in groups. They don't typically fare well in communities because it's difficult for them to compete with fish for the food. Fish see the food and frogs take longer to find it by smell. With WCMM I wouldn't be so worried about that. I don't think they are really the kind of fish that eat off the bottom much. I'd be more worried about the frogs potentially catching the fish. The combo may work, but it does have it's risks.
6 is the minimum you want to stock for most schoolers, so I'd for for atleast that many of the WCMM.
ADF's need to be kept at around 80 degrees. I believe that will be too warm for the WCMM, but since I don't know too much about them I'm not sure, it may just be that keeping them at that warmer temp will shorten their lifespan. Definitely don't keep the frogs at cooler temps though.
Mystery snails get huge and make giant waste, so you'll need to keep a close eye on your parameters if you're adding one to a small tank like this.
Do you already know about cycling? It's crucial to understand the nitrogen cycle and how to make your new tank safe for fish. You'll need a master test kit. Here's more info on that:
The Aquarium Nitrogen Cycle and
The (almost) Complete Guide and FAQ to Fishless Cycling. I recommend you do a fishless cycle if this is your first aquarium.
With your 8 gallon limit you may want to check out the 6.6 bookshelf tank at Petco. It's usually on sale on their website. It's pretty nice, my favorite of my smaller tanks. It's atleast as long as a 10 gal, so it feels much larger than it is. It has a fl tube light which makes it a decent little med. light set up, great for many plants.
If you do decide to go with ADF's you may want to avoid the kit, or change the filter out. Frogs can become stuck in the filter intake of power filters and drown. Something I have experienced myself. I highly recommend a sponge filter for frogs.