First because guppies and tetras are schooling fish your going to NEED at least six of each kind or they may get very stressed and get dieased or even attack each other such as niping at other fishes tail. Catfish, depending on what spieces you get can a may be aggresive towards your other fish, and might eat them. Just stick with one kind of fish at first make sure all are thriving, then add the next species remember not to over stock or they may get stressd again.
Good luck, hope this helped
Good luck, hope this helped