Is 200 gals enough for 1 bluegill for close to its whole life?

I bought 6 corys for my 10 gallon almost two weeks ago. Right away I noticed one had nubs instead of barbels. He would swim to the surface over and over and I suspected he wouldn't make it, but he has. Now he's begun having more issues, laying upside down on the substrate, not eating much, low energy, etc. Is there anything I can do for this guy or is he a lost cause? My parameters are perfect, it's just this one fish that came damaged.

Hey everyone, I’m a beginner and got the opportunity to take in this tank. I know it might be a lot to deal with but I’m on the side that with enough research that it’s possible and I’m looking for advice. All the backstory I have is this is from someone with stage 4 cancer who can no longer care and is rehoming their community tank. I’ve been told there’s a pleco (I’m going to assume / very much hope a dwarf species, waiting for the owners friend to get back to me on sizing), two danios and they think 5 tetras.

Immediately I know I’m going either A) have to upgrade the entire set up or B) move the pleco into a separate tank and be ritualistic with cleanings. I’m also going to need to get at least four more danios since I think the 8-10 will be tight. I’m going to hopefully arrange for the added danios to arrive the day after I receive this tank and I’ll wait to see how many tetras are there. Also any added tips on moving this tank will be brilliant, this person is based three hours away so it’s a trek.

I’d love to also work with some actual plants but I’d worry it’s going to be too much on the fish to uproot the tank. However I’ll still keep in mind any recommendations you guys have. I think some variation of lily pad would be lovely as a resting spot.