If you have any power cords above the plugs/outlets make sure you have a drip loop. I happened to start a fire with very little saltwater getting into my outlet. I'm glad I was standing right there when it happened. There were literally 4 inch flames trying to catch the sheet rock on fire, which obviously didn't combust but it did heat up the outlet cover enough to slightly warp it. It all happened when I left a towell on top of the tank bracing and didn't realize the corner of it was in the tank. It started wicking water and it was laying over my tunze cord and dripped down and ran into an outlet that I hadn't converted over to a GFCI yet either. I knew saltwater was conducting but until you see how fast flames can erupt, I think the mind sort of says "It's water, it can't burn." Then you see that thing arc and the insulation on the wires and the plastic in your outlets easily combusts.
When I moved my tank in-wall and put my sump in the basement, I mounted my outlets and aquatronica power strip on the rafters above the sump and to the side of it. I also made sure there are drip loops in case water from the floor above leaks and runs down the cables going out to the lights and in-tank tunzes etc...
Definitely stress relief the pipes. You have relatively long runs without any bracing. If you have rigid pipe going from your drain hole in the tank or going to the outflow from the pump, you are at serious risk of cracking the glass between the two holes drilled in the bottom of your tank. I have a tank that suffered that. I repaired it easily but it leaked until I did that. That all happened from a mild bump of one of the pipes and it was 1/2" glass. I personally used silicone tubing more than rigid plumbing for the drain and from the output of the pump. I can move it out of the way for easier maintenance and it's a lot cheaper than buying unions etc...
I would go with a bigger sump and an in sump skimmer. Murphy's law that at least once you'll knock your collection cup into your sump. Also any leak in your skimmer plumbing may not leak back into your sump. The more potential leaks you can avoid, the better.