You will have a set up very similar to mine, except the internal overflow which will be very nice.
I run a Mag 9.5 on my new 75 reef tank, although I have some of the water diverted over to refugium, not enough to really count.
A Mag 5 would be way under rated in my opinion.
I'd get the 9.5 or live with risk of problems with the 7. I've never used the 7 so I can't add anything to that delima.
You may want to add a ball valve or tee under the ball valve with another valve coming off that tee. This will allow you to not only throttle back on the return to tank, but allows some water to be recirc'd back to sump. This may help with backpressure issues and keeps the sump moving pretty well too. Not a must - just a nice.
SR4 up to 120 gallons 7.75" x 7.75" 4" diameter 24" height - nice CPR protein skimmer for the price - make sure you have enough room under tank. But a fair unit - I've seen one, but don't use it. I've used Bak-Pak and SR-2. Both under rated for much over 55 gallon tank - but they do work. I would imagine the SR4 would work equally if not better.
IMO - there are no other powerheads worth discussing besides MaxiJets. They are a great design, quiet, put out a lot of water for their size ... and flat out work well. Nuff said, but do as you see fit.
The lighting - again like mine. I currently have 260 watt PC's in a hood, 2 day 2 blue. They are okay in my opinion - not the greatest my any measure - but do allow for a decent number of medium to low light corals. I plan to supplement these lights with MH in the very near future. But they work - and depending on the price, they are not a rip off as far as performance - not the greatest - not the worst.
I agree 100% with what fshhub and golfish
have said - good advise from a couple good reliable members here