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Can some of you experts here outline a method aimed at eliminating several of the pathogens that may be present on a newly acquired catfish fish, before symptoms occur??
The idea is to have a procedure to help to further reduce the risk of future problems, and to be completely effective and avoid re-infection they must have been applied to all fishes in a given tank

Don't!! The whole idea of quarantine is based on the fact that you should observe your new fish for a while in the same conditions as the ones in its future home (the tank it is supposed to live). Aim of the observations is whether your fish is healthy or not. If it stays healthy for some weeks, put it in its tank. If it turns out to be sick, then treat that specific disease.
I mean, I take it you would only take asperines when in some pain and not taking them all day for just in case.
But this is of course just my opinion. There will certainly be more reactions.
BTW: how is fowleri getting along?

Being that most of the catfish we see in the hobby are wild, their trip to your tank is an arduous one. The fish in many instances are in a weakened state. In my view the added stress to the fish from medications is counter productive unless there are visible signs of disease. As Marc stated a quarantine tank is for observation.

Mark