Two of my fish tanks are currently empty.

Currently, two of my fish tanks are empty. The larger one is 55 gallons, and the smaller one is 20 gallons. I'm thinking about adding new fish to these. I've realized that I prefer setting up the tanks; I'm not a fan of bare-bottom tanks.

Currently, I'm trying to do the following:

*20-gallon tank:
I'm planning a blackwater setup in a more natural way. I haven't had any blackwater setups in the past, so this time I'm trying to set up something like this. I'm still not sure what type of fish I need to try.

*55-gallon tank (4*1.5*1.5)
For this, I'm trying to select the fish first and set up the tank based on the fish's needs. These are currently on my priority list. I have to choose one from these:
Channa aurantimaculata, also known as Golden Cobra,
Geophagus tapajos,
Freshwater moray eel with suitable tetras,
Rope fish, Bush leopard, and so on.

Any suggestions are welcome