I've heard of discus fish in planted tanks - it's just that this tank is so large to light. I found a link below that shows the light fall off to the square in general.
http://petapixel.com/2016/06/02/primer-inverse-square-law-light/
For a high tech planted tank:
You would need high-powered LEDs to get good light at depth and even LEDs can add some heat. On my tank (150gal) I don't bother with a hood any more and it's only 2.5ft deep. The CO2 bottle I use is 2ft high so has to sit next to tank. I'm not against doing a planted tank just thinking how the various techniques would work and high tech I'm struggling with for this tank. But would love to see it done.
I like the discus idea as I think a flatter fish would preserve some depth to your tank as it is very tall and wide but relatively not as deep.
I don't keep saltwater fish so can't comment there.
For myself, I'd look at doing angelfish in the tank to start with. You can get some excellent colours, should be fairly hardy and they are also a flatter fish that get to a good size. Some other algae cleaning fish, etc but the angelfish would be centre piece.
Then I'd add a lot of very tall driftwood branches to near surface and tie on some plants near existing lights and just try them to see how they go. Would experiment with a few spots. I'd also see if I can get some spotlights sitting at bottom of tank to light the plants and also give them a bit more light. So a low light, less work tank. (I know I'd be tempted on trying some plants in substrate so would also get a suitable plant substrate). Some thoughts, fish options are more limited here, lots more you could do.
One other thought is that I'd suggest getting a small hospital tank for somewhere. Say 10 gallons for freshwater. If a fish gets say a scrape or been fighting and some fungal or bacterial infection results, would be easier and less expensive to treat in a small tank.