1)Advanced Acrylic made the acrylic canopy. They also made the sump and ATO for me. Basically, anything acrylic, I tend to consult AA.
2)I'm not sure if sand helps with cycle or coraline. The tank did not goes through a cycle since it was basically a transfer with a lot more water added to it. The rocks were in the rubbermaid sump that was running with the temporary tank since May. I mixed in the dry sand because I couldn't find the Special Grade in live and I didn't want to wait. So I get as much live much as possible and mixed it with the dry.
3) The tank has been running for less than 6 weeks believe or not. It's still too early to say I like the G5 over the MH/T5 combo. I will say this though, if I had my old Geisemann MH/T5 Spectra fixture, I wouldn't hesitate to use it on this tank. But I will also say this. The 5 G5 draws about 350W total. That's about the same at the 4 T5s in the Geisemann fixture.
I think for the first 6 months of any tank, my goal is to keep stuff alive. The colors will come later. So far, I'm having great success with keeping stuff alive. However, the colors are hit and miss. My Jason Fox Flame is nothing but a red acro right now. Lost the yellow tips. My Homewrecker, Walt Disney, and Orange Passion are all just green Tenuis you see for $20 a frag that nobody wants. LPS are mostly going good. Questioning some color loss in my green acanthophyllias to too much light(?)
If you're starting a new tank, look into LED. MH is dead and will be a extinct like the dinosaurs. It'll soon be a reality whether you like it or not. If you're running MH now, be happy and keep running it as long as you can. But know that time is running out on MH. Whether if it runs out before you quit the hobby, who knows.