As far as the frogs are concerned, you need to know which species you have. The two commonest are African dwarf frogs (adf) and African clawed frogs (acf). The dwarf frogs have webbed feet front and back, and their eyes on the side of their heads. These frogs do not grow very big and will only eat fish fry. Clawed frogs have webbed feet on their back legs but not their front legs, and their eyes are on top of their heads. They grow quite big and will need large tanks long term - and they will eat fish.
I have a dwarf frog. These guys don't get very big, and because they are air breathers, they need to be in a tank no deeper than 12, maybe 14 inches. Being so small it takes quite a lot of effort to reach the surface and if the water is too deep they'll have problems. The main problem with keeping dwarf frogs in an aquarium with fish is making sure they get enough to eat. They are almost blind and find their food by smell - by the time they find it, the fish have eaten it all. Despite what the shop said, food like bloodworm and shrimp are best fed only once a week as a treat. the rest of the time they need special frog food. Depending where you are, look at HBH frog food (USA) or zoomed frog food (UK). I had to get my zoomed food on-line as I couldn't find a shop that stocks it.
I've found the easiest way to feed the pellet food is to hide it in a cave - ie an upside down plant pot which has frog sized holes cut in the rim. I soak the pellets in a bit of tank water then suck them into a pipette and squirt into the cave. The frog can get in there but the fish can't. With bloodworm, I defrost in some water, suck a worm half into the pipette and stroke the frog's nose with the free end. It soon realises what it is! This isn't quite as successful with brine shrimp as they are the wrong shape.
Make sure your tank is escape proof. I did have two frogs but found one on the other side of the kitchen. It did live for another six months after its escape, mainly due to the good advice from jenste after I posted here in panic. All holes are now plugged with filter wool.
I'll let someone else advise on clawed frogs and apple snails.
bit of an algae problem and the frogs were in with the snails and i just thought they looked quite cool, asked about them and alls they said were that they just need bloodworm/brine shrimp which i already have for my fish 
