Your situation is very complex and has a ton of variables that affect your outcome.

I feel your filtration may be a bit vulnerable and would want it to be redundant so there would be no way to expose them to ammonia or nitrate situations which they do not tolerate.

Disus are a very difficult fish to assimilate into an aquarium because they come from uncontrolled sources in most cases. A fish that appears to be in good condition in a shop may be in that condition because of medications or special acomodations.

You want fish that have been in a stable environment very similar to the one which you can provide with ease. The more tampering you are required to do the most chance to cause them stress. When buying Discus from a shop you want to be very much in the know on signs of problems. The fish should be in their coloration and not darkened, they should be shy but not overly so. They should accept foods in the shop per your request. The water should be near the average for the waters required to keep most other fish in your area. You do not want to buy Discus that require a ph of 5.0 and straight RO water unless you are well versed in their care.

While it is true that the majority of Discus will require special conditions you will find that certain strains are more domesticated and more readily accept a bit harder waters, a bit higher ph and are a bit more accustomed to domestic life. There are types that will just straight drive a guy crazy too. Patience is hard to apply but will serve you well when selecting your first Discus stocks.