New to large fish...

Before I start let me just say that I didn't know exactly where to post this so if a mod could move it that would help me so much.

Anyways, I'm ready for my new fish tank soon and I just thought I should plan ahead. I don't know much about large fish and have only kept fish that grew to 4-5" before this and thought I should try something new. I know that these fish are going into the tank:
1x Red Oscar (Or Lemon)
1x Leopard Sailfin Pleco

I was also thinking these fish as companions:
1x Flagtail Prochilodus
9x Red Hook SD's
2x Lima Shovelnose Cats

I don't want too much stocking because I only want to do 20% w/c weekly. It will be a BB tank with like 10x GPH of tank volume/ hour.

I want fish that live in medium flowing warm-ish clear water streams in their habitat so all the fish will thrive in the same conditions. PH around 6.5-7.2 (Doesn't have to be exact, though)

If you have any ideas feel free to respond.
P.S. It is 180 gallons 72" x 24" x 24"

1x Oscar
1x Sailfin Leopard Pleco
9x Red Hooks
1x Flagtail Prochilodus
2x Lima Shovelnose
Would that be overstocking in a BB tank with a wet dry filter/sump with Mag drive 18 (1800 gph) and an Eheim 2262 filter (350gph) rated for 400g fish tanks? 20% w/c weekly.

I don't want the fish to be stressed but I'm not sure how well they work together and how much space each fish needs for territory. Please tell me if the above ^^^ stocking would be alright and if I'm overcrowding with this list.

Really. Even with just the Oscar and pleco and mass amounts of filtration... Ok. What about 30-35% w/c every week?

I figured the sump/wet-dry would add volume to the tank size and convert everything to nitrates because of how much bio-media they have, and then the canister would handle the mechanical side of the spectrum.

To be honest I'm not even sure about the shovelnoses, they seem very skittish from what I learned about them and also very boring.

So it's not even possible for 20% w/c weekly. Like I said in my last response, would 30-35 be enough for just the oscar and the plec. Sorry for double posting.

Thanks DMD123 for that. I really didn't know their exact size. I know about spotted silver dollars but those are too small and may be eaten by my Oscar.

I want slow-er movng fish. The spotted silver dollars aren't as active apparently. The Oscar and Pleco are garunteed.

Ok, I think I have found something that will work:

1x Oscar
1x Sailfin Pleco
6x Red Hook SD's (Found out they can be slow moving, too!)
Possibly 1 FT Prochilodus

Flagtails are HUGE!!!
[video=youtube;opuxX_55SNI]https://www.youtube.com/watch?v=opuxX_55SNI[/video]

Could I keep a flagtail maybe? I've seem it done ^^^ but not sure if they do well with oscars.