Most important thing I found is that you will have 1 or more than 5 Discus, nothing in between.
For a 75g I would get 8 Discus, make sure that they are all of similar size when you buy them and make sure you have some decent size plants/wood in the tank.
The reason for the plants/wood is to break up their line of sight so that even with their pecking-order, the lowest one will still be able to easily pickup food out of sight of the other ones.
Popular belief has it that Discus are very difficult to keep. I would say that's not entirely true. 2x 30% water changes and good bio-filtration (2 Canisters or a sump) should take care of your water for that.
Last, diet: I used to feed them blood-worms, but I'm now on 100% dry food. The risk of Discus picking up worms is relatively high, and feeding them dry food is helping to reduce that risk while giving them all their required food-contents.
Temperature at 28'C minimum, they will have no problem with higher temperatures but lower makes them slow down. (Treating a sick Discus, I normally increase the temperature in the med-tank to 33'C while on meds).
In general, beautiful fish that are not much hassle. You'd might get them used to being hand-fed, though I don't bother with that. Feed them regular (ideally 4 - 5 times a day for juveniles) dry food comes easier for that with a feeding-machine that you clip on the side of the tank.
For adults, 2 - 3 times a day is enough.
Watch their poop, it is the best indicator of sickness. Dark brown or almost black is ok. light/white indicates worms or other parasites.
Good luck, enjoy them and just take care of the water-changes (which helps the rest of your tank as well.)