Think 50 gallons and upwards for a minimum of 5. You'll need to use soft water that is slighlty acidc or neutral and you'll need to keep it at 29-30C. Find a shop/breeder you trust and match their water conditions for best success. You'll need to test your local water and you'll probably find you need to soften it, mixing in RO water or using RO with additives is the easiest and most consistent way of doing this, and consistency is very important when keeping Discus. If you keep the water parameters ok your fish should thrive.
If you've only been in the hobby for 5 months I'd say do this very slowly. Research everything in detail and decide if your prepared to put the effect in to keep these wonderful fish, some people aren't. I do two water changes per week for my Discus and they are fine, I know people who do less, and I have read about people doing a lot lot more.
You can buy from a petshop if the fish are high quality, you want a nice round Discus with eyes in proportion to the body and it should be alert. If you can find a decent breeder then go for them instead.
Its not true Discus do better in pairs, unless you want to breed. They are a shoaling fish and should be kept in groups. If a pair forms a bond then they kept in a tank on their own, but only a bonded pair.
If you want to buy small Discus then in my opinion a bare bottom is essential. Having said that I use a bare bottom tank for Discus which are larger. It makes things a lot lot easier. I buy all my fish at around 3-4" now though as I find they do a lot better at that size.
