Hi DanielH, you need to watch the advice on Discus here you get alot of bad replys from people who may not even keep discus but have jumped on the band wagon from other peoples advice.
I have and know lots of people who have kept all sorts of fish with different numbers of discus with no problems, if you do buy them small just keep on top of the feeds and water changes and you'll be fine, thousands of people won't even do that most LFS will sell discus to anyone without asking a single question about set up.
That said discus will be easier to keep if you but biggest and most you can house and afford, just feed little and often with lots of nice water changes!