Well, I don't always weigh in on sumps because I don't have one, lol. I might have some ideas though. So, how about some mechanical filtration? I'm not sure how your sump is set up, (perhaps you could post a pic?) but there are several options for this.
Mechanical filtration should be kept pretty clean, or else it just holds on to detritus and ends up releasing more nitrates into the water. So, if you were to go with a filter sock, you'll need a few so you can switch dirty ones out for clean ones. Sponges, pads, and mesh should be rinsed or replaced in the case of flossy single-use type stuff.
I'm not sure what your stocking plans are, or what nutrient level you'll want to maintain in a FOWLR. Just like in freshwater, low nitrates are fine, but yep, excessive nutrients will, of course, lead to algae. The skimmer should help with nutrient reduction, but if your plan is to stock heavily, or you just want to add another form of nutrient reduction, then you might be able to set up a refugium in the sump. You'd need an area to contain chaetomorpha, a macroalgae that uses up nitrates for growth, and you'd have to put a plant light over it. It's fairly cheap to implement... if you've got the space.
You can also put rock rubble in the sump. This would be a good place for copepods to colonize and thrive, and thus, provide a good source of yummy snacks for your fish.
You could also look into something like this...
Again, I'm not experienced with sumps, but I know there are lots of options out there to optimize that space to meet your goals.
Sorry, I'm just not the one to talk to about lighting. The hubs is good with that stuff, but even with that, we made a mistake with our first light, then spent months agonizing over our LED purchase. Look at lots and lots of reviews and see if you can find other aquarist's experiences with that specific light. You probably want to look at some of those other forums with bigger reefy crowds.