Hi and welcome Nick .
Your plan of seting up the tank first , let it fishless cycle with Amonia and maybe a bottled bacteria and adding your discus after a month or so , sounds reasonable to me , of that's the only tank you have to work with .
Without having other fish In the tank to worry about cross contamination you can safely put your discus straight in the tank .
One important decision IMO would be to add a couple of bucks more to your current investment and buy 5-6 inch full grown discus instead of juvies .This is important since you are a first time discus keeper and because you want a planted community environment , which can be more chalenging for discus health .
Good luck and please keep us informed about the process of setting the tank and do send some photos of your discus , once you get them .