Try running it with the Mag 8 first. I had to dial down my Mag 9.5 when it was all said and done. Yes, I would guess that the sump you have is setup for an external pump like a reeflo. Plenty of people run external pumps without issue and hopefully they will chime in as to the pros and cons. I think one of the advantages of an external pump is that you don't get as much heat transfer to your water. Of course, there are DC pumps these days that use minimal power and running LEDs takes care of one of the biggest heat issues.
Personally, I am a fan of AI lights like the Hydra 52 and Hydra 26. You can find previous generation used lights as well and save a bit if you look for the AI Vega or AI Hydra lights. I like the control options, customer service and support, mix of colors, and the available upgrade paths (although I always seem to just sell my old fixtures and buy new ones) available in the AI lights . Lots of other people have great success running Ecotech Radions, Maxspect Razors, Kessil pendants, Reef Radiance LEDs, doing DIY LED builds, etc. There are literally hundreds of options out there and it just depends on what type of budget and features you have in mind.