watch the video in the beginner section too, it is very informative.
just some thoughts:
1) get all ur discus from the same supplier at the same time to avoid cross contamination issues
2) there are excellent sources for discus on this site which have been vetted and have good customer service
3) starting off newly with discus and substrate is difficult, esp if u r planting a carpet, if there is any way u would consider doing a bare bottom tank at least for the first little while i really really recommend it (i wish i had done it) - even more essential when starting with younger discus. u can always add the substrate and decor later. i know u already have the plants and are eager to add them and dont want to hear this but i gotta say it anyway, just from my own bad experience
4) a quarantine period in BB would be a good idea, if u arent keen on a BB tank in general
5) RO water and additives may not be needed, depending on ur water parameters - can u provide ur tap water parameters straight from tap and then fill a bucket and aerate it for a day and retest and provide those parameters as well (aging water may be needed)
excited to see pics! maybe start a tank journal thread and track ur progress! welcome to the forum