Hi Helium_Junkie
You can keep ADFs either alone or in groups; it doesn't really matter.
As for their tankmates, they will be fine as long as they are kept with small, non aggressive fish. If you look at their little arms and avoid anything that might be attracted to their waving and think of them as dinner, you should be OK.
Another thing to consider is that they are jumpers and must be in a closed tank. They are able to escape through some very small openings. You must also protect them from being sucked into a filter.
I like to keep them by themselves for their own safety. I have two of them who have been living happily in a one gallon jar for some time now. They do not need a filter and can do just fine with weekly water changes and an occasional good cleaning.
When I do this, I remove the frogs to a pot of dechlorinated water, empty the water and decorations from their jar and just swish some fresh dechlorinated water around in the jar. This washes out the gravel while keeping the beneficial bacteria. I then refill the jar with fresh dechlorinated water, replace the decorations and put the frog back in.
Just take care not to overfeed them so that extra food spoils at the bottom of the tank and all will be well.