Please do your research before you buy fish. I'm trying not to be too critical here but you are quite overstocked. I tend to be a lot more conservative with stocking than most other people, but these are cichlids, some of the smartest fish out there (particularly the oscars). They need a lot of enrichment and even though they are not too active, they need a lot of room to explore and swim around.
In particular, you will need to watch out for aggression. Your jack dempsey may be very aggressive to the oscars and the oscars will return the aggression. You need to cycle your tank, otherwise your fish will be gone within the month. If you don't know what that is you need to look it up (you should have already done so, if you followed fat homer's advice).
However, you did a lot of things right. The tank size is satisfactory if you get rid of your pleco (do not release it into the wild) and preferably the JD as well. You have a filter and a heater, and for beginners that is a huge tank and huge fish. Don't beat yourselves up too hard if you lose one or two (considering your tank is not cycled, this will almost certainly happen), you are beginners and this is why I don't recommend starting out with such an expensive investment. But this is what it is and you might as well make the best of it.
One more thing:
The moment ammonia or nitrITE (not nitrATE, very different things) rises above 1, dose the tank with seachem prime.