I suggest going slow and easy to start off. Your first cat choices aren't the easiest cats to keep. Columbian cats are brackish water cats. Channel cats do better in cooler temps and high DO levels. Raphaels are nocturnal feeders that can easily starve if you don't target feed them in dim light.
The plecos should have done OK. Did you have any driftwood in the tank? Plecos don't actually garner nourishment from the cellulose. They gain simple sugar nutrients that are the byproducts of bacteria that inhabit and feed on the surfaces of the wood. Also, depending on species, not all plecos are solely herbivorous in their feeding habits. Quite a number of species are omnivorous and require additions of meat proteins to their diet.
For a large number of riverine species, you want to add a good rate powerhead and focus a current of water towards the bottom of the tank to increase the DO at the bottom. And, most importantly, ensure those twice-weekly gravel washes/waterchanges are accomplished. The more "gunk" on the bottom, the greater the chance of reduced DO, increased ammonia, nitrates, and nitrite concentrations for the fish to have to deal with.
