From your first batch of pictures your overflow looks like it is setup corerctly in that if a power outage occurs you shouldn't have to worry about a siphon break. They are designed so that when the power goes out water will stay in the collection box inside the tank and in the inside chamber of the outside box (if you follow that). So that when the power comes back on the siphon should pick right back up again.
There's two tests you want to perform with your sump. One to be sure your siphons are set up properly and two to determine you maximum water level in your sump. To do this follow these simple steps:
Have everything working with a minimum amount of water in your sump.
Mark the water line in your sump.
Turn off the power and let the water in all the plumbing settle.
Mark the new water line in your sump.
Turn the pump back on and watch your siphon closely to be sure it returns to a normal operation.
Once your test is complete you now know how much the water level in your sump will rise when the pump is off (either for maintenance or a poweroutage). You will want to set your maximum water level in your sump to be that distance from the top of your sump (give yourself some roome for error here)
In regards to you skimmer... thats an interesting design. I can see it now in the first set of pictures you listed... it does seem like something is missing though. The way skimmers work is you want to maximize the time a bubble of air is in contact with water before eventually rising up to the collection cup without escaping back into the rest of the water volume.
it seems like there should be another cylinder that comes down through that triangle bracket at the bottom of which you would put a wooden air stone or plumb a pump with an aerator... got any extra parts laying around your not sure what they're for?
The picture of you holding the collection cup, the holes in teh top of that I would suspect are simply vents to let the air from teh skimming process escape since the lid to that looks rather secure.
For the light, just a minimum amount of light is all that is needed. This just helps algaes and such grow on the rocks to contribute to its benificial processing of nutrients in the water. Lots of folks also include forms of macro algae in their sump/fuge to further add to the nutrient export. A small PC
light over the LR
section would be fine. if you wanted to put a bit more lighting on there and maximize the LR
/algae exposure you could set the lights in the sump to be on opposite the lights in your main display. A lot of folks do that to help balance the pH levels in the tank over night.