You're on the right track, but a little light on the number of discus - 5 fish is usually the minimum recommended number to maintain reasonable pecking order harmony - and 46 gals is on the small size for keeping 5 discus, but certainly doable if no other tank-mates are included. Consider moving up to 60 gal or larger if feasible, and get 6 fish.
4.5" discus is a good size to begin with as a novice discus-keeper - they are near adult, have fairly well-developed immune systems, and are much more tolerant of less than ideal water quality and occasional lack of attentive daily care, than any smaller size than that. The added cost of larger fish over younger, smaller specimens is well worth the lessened risk of keeping them healthy & thriving.
It's a great idea to limit any décor, so your planned light sand layer and moderate rockscape is well considered. Minimalism is key to allowing for easy tank cleansing.
Best of luck to you.