Wish I were so lucky as to find the great deals you have...minus the poor fish, I hate that. =( Some people just suck, but you really did get a good deal, or so it seems thus far. You have a talent for this stuff. Once the work settles down, I hope you can actually sit and enjoy your tanks with their regular, much easier maintenance!
If your first tank that you rescued is cycled or close...add in a sponge with your current media. Leave it there for a week or so and let beneficial bacteria colonize it. At the end of this time move 5-6 gallons of water from your original tank(should be cycled by then I should think since you were sent mature media, if you didn't kill it with tap water...even treated there's a risk always wash in removed tank water GENTLY), add the rest as treated new water(or you can add all ten gallons from your large tank), and put that sponge in the ten gallons filter. That should help cycle it either immediately, or within a couple days. =)
Helping cycle your tanks...I suggest you request mature media from others again. Don't wash it this time and you should cycle pretty quick. =) Can't see much of another option at this point since you are relatively new to it and don't have a fully cycled/stable or well established tank to take mature media from to help your other new tanks.
Your pleco is a bit skinny, but from that angle seems alright. Underlying issues are a possibility of course. =/ Keep him apart from others for at least 4-6 weeks at the minimum and observe him. He could be carrying any number of nasties you may not spot for a while, like parasites which are a major you know what to get rid of.
That suckerfish looks like a common pleco(we would need a side view photo to tell you for sure, or at least give valid guesses), they get 16-24 inches long and are thick bodied. Here's one in a 55 gallon, just to give you an idea of what else you got yourself into...considering how you're going at this, I wont be surprised if you take a step up later on(it'll take him a couple years to get this big, don't worry, and he shouldn't stunt in a 55 gallon, possible but he shouldn't, it just wont be roomy then...). Or perhaps a Bristlenose pleco which would be so much better for you, they stay around 6 inches. Hard to tell, looks like he -may- have whiskers and that face shape, but he could just be a skinny common too.
I named a lot of foods on your original 55 gallon rescue tank thread that he will greatly enjoy, especially the cucumber, zucchini and steamed/boiled broccoli stems. Just you make sure it's all nice and squishy, and remember he is a catfish, not really a sucker-fish, they are omnivores and need more than just algae. Fed on only algae and algae products he will likely be malnourished and not healthy. Proteins like brine shrimp, mysis, glassworms goodies for him. High quality algae wafers too, he should get a small chunk a couple times per weeks, and high quality veggie flakes sunk down to him will also be good.
Here's that vid of a pleco once full grown, or close to it, in a 55 gallon tank, that 200 gal would certainly be perfect, anything around 100 or more gallons would be better for one, though it's do-able in a 75 bigger is better: https://www.youtube.com/watch?v=P_ui-nmEmrE