Watermelon, zebra, gold sunshine are my 3 top favorite plecos. The watermelon i had wasn't too long, maybe 14", but they are a very wide headed species of pleco. Driftwood eaters too, so not a good choice if you have some nice driftwood. Turtle and pleco is an interesting combo, Ive never kept turtles with fish before. I had some Eastern Painteds before but never with fish. IF you check CraigsList you may be able to find some nice deals on a 90 gallon. I got mine new from glass cages, big mistake on that one. Cost almost 800 dollars with tank and stand. Plus filter and equipment and I was already past $1K for a single tank. As for the trout, I get them at a local hatchery for 50 cents an inch. The have all kinds, beautiful trout. Golden is my personal favorite, but they are all so beautiful. I have Tiger, Brook, Rainbow, and Golden Rainbow. I overstock all my tanks, so I have about 10 8-10" trout in there. They seem happy enough. In the hatchery you have the trout crammed on top of each other. I think you could get away with inch per gallon with a UV sterilizer and dual filters. Thats what I have, 2 aqua clear 500's and a (expensive) UV sterilizer. On top of clear water you have to have current, so throw a couple powerbeads in there too. They are a very active fish, and love to swim against the current of the powerhead. With a nice light, they show great colors as well. ….and don't even get me started on piranhas lol. Love those fish. Maybe one day I'll get some more. I have had Red bellies, Caribes, and Elongatus piranha in the past. You can keep the Caribe and Red bellies in a school, but not the Elongatus. There are 2 main genus of piranha, Serrassalmus and Pygocentrus. The Serrasalmus are the more aggressive ones, have to be kept solitary(With some rare exceptions). The Pygocentrus are the less aggressive, but still very aggressive, schooling Piranhas, and the more well known ones. Pygocentrus Natteri, or the Redbelly piranha are the iconic piranha that everyone thinks of when they hear "Piranhas". They are the ones from the movies lol. I suggest if you're interested in getting piranhas, get a 40B or 37 Tall and growing out 5 caribe piranha, then thinning them to 3 piranhas when they get 6". Dim lights, low pH, plants and lots of cover, amazon extract in the water, you'll have yourself some nice piranhas. You can feed goldfish on occasion. Stick to frozen foods like silversides for the most part. Goldfish can be fed as a treat, maybe once or twice a month.
Sorry for the rambling haha. I love talking about fishes. Almost as much as goats and chickens