The question is, which are you gonna focus on?
If you are able, buying 4.5-5"+ discus will increase the discus tolerance of less than pristine conditions in a planted tank as they are already beyond the rapid growth phase. They're more expensive because the hard work has been done, but IMO well worth the money. I spent $640 on 8 x 5" discus and love them.
In your situation though you still have the QT issue to overcome since your tank already has other community fish in it which potentially harbor pathogens that could make your discus sick. Mine all came from 1 reliable source and are in BB tank with some wood and a few rock only. I have had 0 issues since my purchase from Dennis's discus fish 3 months ago.