Haven't cut a hole yet, but we will this summer. I was going to buy a hole saw the right diameter - I'm guessing 6 1/4" without measuring the fan.
I would cut the hole as close to the center of the roof line as possible, or at least stay away from the sharper curves of the roof line. The flatter the roof where you cut the hole, the easier it will be to seal around the fan.
For power, you can probably tap off an existing roof vent or ceiling light fixture. You should be able to find a 12 VDC wire to splice into and run to your new fan location. You could try and run it above the ceiling, or you could install a small surface mount wire chase and run the wire in that. If you ran the wire chase next to some ceiling trim strips (if there are any), I bet it would blend in fairly well.