A sump is mostly useless, and will be problematic if you decide to add CO2 (which you will need if you keep yout current lighting because it's really strong) because all that water movement will make CO2 escape from the water. I suggest you plug the overflow's drain and place equipment there, like your heater and filter's intake. Or better yet, if you have access to your house's plumbing, you could connect your overflow's drain directly on your house's drain, with a solenoid valve controling it, so you can have automated water change. That's what I did, I could give you more details if you want to do this.
If I understand, you don't really have a filter, only the sump? I suggest you get a Eheim 2217.
Your lighting should be good to grow plants, but there is probably too much blue and that doesn't look good with plants. I know because I am using my old reef's LED lighting, and it really looks bad with the actinics on so I just never use them. But the plants grow extremely well. But as I said, reef lighting is very strong so the use of CO2 is necessary.
Also, from what I know discus don't appreciate strong lights.
You probably have a RO/DI unit, that will be very usefull to replace evaporated water. I use it for my 20g which I almost never do water changes, if I used tap water for topoff that would increase the hardness. So, tap water for water changes and RO water for topoff. And you won't need the DI stage anymore.