I may be a dummy...

Ah so much to talk about, Oscars do nap, but IME not usually at the bottom of the tank usually they camp out or lurk in a favorite spot suspended. Lying on the bottom is not always but usually a sign of stress.
First of all be prepared to answer many questions, and take some flak. there are some great minds and experience levels here, and people will tell you their thoughts. Just remember what is done is done, learn what you need to to correct and improve situations.
Before we can help with much of anything, we need some information. Tank size, ammonia, nitrIte, and ph will be a good place to start. You will very soon also want a nitrAte test kit and you really should get a kh test kit. If you are 72 hours into this, with four or 5 fish unless they are babies and this is a 150g tank, you are in for a lot of work.

Any idea of what kind of Plecostamus you have? If it's a common, it will grow quite large, your oscars will be 12 inches in a year most likely, and the labs Will be pretty much incompatible due to size and temperment of all fish involved. It is also highly possible if your Labs aren't three inches long by the time the oscars are 9" the labs will become lunch.

You will essentially need about 90 gallons minimum for two Oscars and a plec. IMO you would be better off with 125 or so for these three.
I am purely guessing here but I think you have what some people call yellow labs which are also called electric yellow hap. this link will show you some pictures and give you some info if my guesswork is right.
Electric yellow hap

read the cycle sticky at the top of this page, let us know tank size, ammonia and nitrite right away. make sure you have ample dechlorinator for large daily water changes and don't get defensive when people scold you we were all newbies once.

Yes you'll probably need a much larger tank. Knowing most pet stores, you'll probably want to get those fish back before the guarentee runs out. If I were you, I would take back the oscars and pleco. Of all the fish you have, the yellow labs (or electric yellows) are probably the most compatable with that small space.

Echooooo what Daveedka said: be prepared to take tons of flak and don't be discouraged when you feel like you're being shot down. Everyone that's here is here to help.

And welcome to Aquaria Central!!! Where'd you hear about it?

OK. To increase areation is easy, lower the water level so your top fin splashes more. As far as test kits, I use aquarium Pharmaseuticals liquid tests. The quick strips are IMO not very good. most liquid kits AP and others are fine. During the first few weeks, ammonia, nitrite, ph, kh are the inportant tests in that order as far as I'm concerned. after a few weeks, nitrate, kh, and ph wll be what matters. Be careful what you let the lfs talk you into buying.
Rocketman has a good point with taking the 3 big boys back quickly. It would sure make the learning curve go easier on you as well as the immediate expense. The Oscars grow at about 1 inch per month so you really only have about 45-60 until a 10 is crowded. Oscars are also a messy fish which require excellent maintenance and good filtration. Not impossible as a newbie, but more difficult to learn quickly. Oscars are by far my favorite fish so don't think I'm telling you not to have them, you just need to be aware of what you are getting into. On a bartenders salary, I'd go with Rocketmans advice, and then start saving for a 20-30g for the labs, and then save up for the eventual 90-125 for Oscars. If you enjoy it as much as most of us, in a few years you will have 2-30 tanks anyhow.

It is not uncommon to have two Oscars in a 125-150 gallon aquarium... so just be prepared for upgrading ASAP and be sure you want these fish. They are a major chore, and I would never recommend them for a beginner. But if you really have the gumption to keep these fish, just remember what we say. And read up on them to get all sides of the square.

You could still keep those Oscars in a 30 for 5 or 6 months before you have to move them. And because a Huge tank, (125+) is so impractical, especially as a begginer, you may be better off with a 60. Although I might be the only person on these forums to tell you this...it is possible to keep 2 Oscars, especially one's younger than a year, in a 60G.

The larger aquarium might be impractical for a beginner, but that’s why these fish are not beginner fish.

If this poster does get a 60, I would bet my life that after not too long, they'd have to upgrade (yet again). This constant upgrading is very costly and IMO, more impractical than starting off with an adequate aquarium from the beginning.

Cycling a tank for 36 hours really won't accomplish anything. A true fishless cycle will take a month or so. I would move thos efish over to the new tank asap. Move them with their dirt 10 gallon water as well at the beginning. Then slowly start to change that water out, doing a 30% change each day. Move the small top fin filter over as well as it have built up some bacteria that is important to have.

During this initial cycling stage it is important for you to do daily water changes so that the ammonia and nitrite levels do not raise high enough to damage the fish.

I too would suggest taking at least 1 oscar back as well as the pleco. If it were my tank (the 30) I would keep the yellows, add some rocks (as they like to hide in caves) and possibly add a nice pictus catfish on the bottom, something that gets to be no more than 4 inches long.