New tank owner, I just bought a brand new tank 55 gallons. Have put anything in it yet (even water).

I saw the tetras in the store and fell in love with them. I was told by a friend that platies are nice too, and that it's easy to start the cycle process with them too. Will it be a problem mixing the two, in terms of aggression or water conditions.

Also looking to put a cat fish or two for the algae, any recomendations that will get along well with the the tetras and/or platies? Also considering a red tail shark, but I don't know if it's too big/agressive for the other fish. I am planning on understocking the tank to give the fish more room and keep the water cleaner (hopefully)

I want to make sure I don't do anything that will cause problems between the fish, I figure a new guy will have enough problems beginning anyway.