Stocking a 75 gallon cat tank

[Divemaster]

I'll make this short to not bore people with background. I'm freeing up space in my 75 long (48" x 18" x 20") and want to make it a mainly catfish tank. The base stock will be 6 giant danios, 1 striped raphael catfish, and a gibbiceps pleco I'm growing out since they're already in there and I want to keep them. The giant danios are about 2-2.5 inches, the raph is about 3.75-4", and the gibby is about 4".

Some of the fish I was considering (That I have readily available) are a 5.5" Bagrichthys macracanthus, a 3-4" parauchenoglanis ngamensis, a 2.5-3" Ameiurus nebulous (I'd be growing the bullhead out obviously they get to large long term), and a 2-2.5" synodontis Angelicus. I know I can't get all of them but I'm looking for a good combo of them and the ones I already have. I'm leaning towards getting the lancer and the bullhead plus the ones I already have but that may be overstocked.

Here's my tank specs:

Volume: 75 US gallons
Dimensions: 48" long by 18" wide by 20" tall
Substrate: loose gravel
Lighting: 3:00 PM - 9:00 PM plus ambient daylight
Filtration: Fluval 406 canister, I'm willing to get more if necessary but nothing to pricey.
WC schedule: 40-50% weekly
Temperature: 75-76 F
Ph: 7.6

[apistomaster]

Since you plan to keep a variety of species from all over the world your possible choices are almost endless.
I personally wouldn't stock it with the Ameiurus nebulous(Bullhead Cat). Mainly because it is a coldwater species which has a rapacious appetite, a mouth to match and it's ultimately large size.
If you just stuck with the species you listed your tank would be heavily stocked once the larger species have matured.

[Divemaster]

The gibbiceps pleco is just something I'm growling out until it hits about 10" then it'll go into a 180.

[Divemaster]

For the stock I wound up doing 6 Giant Danios, 1 Striped Raph, 1 Gibbiceps, and 1 Yellow Bullhead.