I should have said go to Tropical fish profiles! Loaches are Cyprinids. Platys are under Livebearers. Main difference is water hardness, and salt requirements. Loaches don't tolerate salt, and Platys almost require it! If you want catfish, be careful about these parameters. Hope this helps.
Welcome! Looked at your tank profile and would advise against combining Platys and loaches. Different water requirements. Go to aquarium fish care and look at differences. Other than that, good luck, and hope to hear from you again. I also am a Platy breeder.(you will be a breeder, if you get Platys. Comes built in.)