I can answer the first. I have a 600w and a 4" vortex. I was running 100' of duct and found the fan not powerful enough to properly cool the lights. I have removed 50' of duct achieving mildly better results. It's apparent to me that I will need a much bigger fan. A 8" perhaps aught to do the job. I hope. I just ran across this in my own research:

Size CFM Amps Watts RPM dBA
4" 172 0.77 80 2500 49
6" 449 0.9 100 2600 49
8" 747 1.42 150 2550 54
10" 790 1.64 215 2510 57
12" 1140 2.42 296 2400 67

To me it looks like the 8" will be enough. It would only be mildly louder. I ended up suspending mine from the rafters but I must warn you that if you bolt it to a rafter, the vibrations will transmit through out the house. Better to devise a way to insulate the vibrations from anything that will transmit the sound.