If you have 5 frogs for a 5 gallon that is what I would consider a max. 1" of fish per gallon is what I was taught (and then there's minor details over aggressive fish), and frogs count as a "fish". If you want to wash the stuff in your tank, hot hot water is great. Freshwater Aquarium Salt is great to provide something rough that could help to scrub. Do not use soap. Soap is bad. It can leave a film that will prevent proper transfer between the water surface and the air. Soap = evil. Hot hot water is usually appropriate. While I don't recommend this unless it's serious circumstances, I have used bleach to clean out fish aquariums. A very dilute bleach, mind, and then rinsed it only about 40 times afterwards with Aqua Plus or something like it (water dechlorinator). Your "spiky" plants are plastic, so I wouldn't worry too much, the frogs will probably try to burrow underneath them. Make sure your lid is secure, whatever you get, the frogs are great at hopping and jumping, an open lightbulb could be dangerous. I've heard of some frogs escaping (and not quite making it because they are aquatic). One more thing before you go... Make sure wherever you buy them from they said "Dwarf Aquatic Frog" somewhere on there. Through your research you probably have seen photos. African Clawed Frogs are not the same thing, they are way bigger!!! Sometimes the Dwarfs will be listed as African Dwarf Frogs or some nonsense by pet stores trying to sell something more "exotic".