Honestly, unless you are just looking for a project, you could get good results a lot easier by just investing in a good canister filter.
If you want to go with a sump, it will definitely work. I just don't see a big advantage over a decent canister.
The place to start though if you go with a sump is how you get the water from the display tank to the sump. If the tank isn't drilled, and you don't want to drill it, you will need to invest in a good HOB
overflow - and they aren't cheap.
You can use acrylic sheets from home depot in a glass tank to compartmentalize it. If you want 2 compartments, I would recommend 3 sheets so you can make a bubble trap, as I mentioned before.
You could also consider a freshwater refugium of sorts and grow some fast growing plants with high nutrient uptake, like hornwort, to remove some nitrates from the water.
You could use biomedia and filter bags in the first compartment for bio filtration, and use a filter sock on the end of the sump drain for some mechanical filtration. You can also run bags of purigen in the sump pretty easily. And it would be good to put your heater in the sump to keep it out of the DT.