A 5ft tank would be fine.
I used to keep Discus & Angels exclusivly before getting into the the bigger guys. I still keep two planted tanks one has 3 wild type Angles in them was 4. I always do a planted tank. I like Crypts on the bottom, and plant Valisneria, Ludwigia in the back and Amason swards as a center piece from time to time. Also grow some Java fern on the drift wood. Water sprite is great to get things going it sucks up nitriates and nitrites like a sponge and is also good floated but growes like crazy. I used Harlaquin Rasboras and Glo-lite tetras also Blue Tetras all at different times I liked the look they gave the tank and get big enough not to get eaten. I liked a black background although I've used the planted looking background too. I used about an inch of plant substrate and small gravel mixed with PFS on top to anchor the plants. I liked using one Bushy nosed pleco and about a 12 Amano shrimp (find big ones or the angels will pick them off) for algea duty along with an SEA gotta find a real one the black stripe down the center will go all the way to the end of the tail. Over my planted 65 I use 130W CP with a 10K/6700 combination light. I'm in work now but if you're interested in what I'm talking about I could post some pics later when I get home. Also a small school of one of the smaller corys are nice crusing along the bottom. I use to, but not anymore keep a mesh bag of Pete Moss in one of the canaster compartments. it was good for about 3 months then I would put some new Pete in. I would get insperation from the T. Amano type planted tanks and for a while I had things going so good I only used a small HOB filter for circulation and to hold the bag of Pete. I often think about doing another elaboate set up actually once everything is balanced it's not too much work at all. There is alittle more to it than what I'm writing here, balancing the ferts, CO2 & lighting but if you enjoy it it's fun and the results are amazing. I don't say much about this stuff because I spend most of my time here in the SA/CA section.