I also am very happy with Velux. I added two of them when I remodeled
my family room. I'd also suggest getting ones that open. They are
really nice for moderate temp days, like spring and early summer. If
you go that route, then I'd definitely get the electric motor kit.
Without that, I'd probably rarely open them. With a simple swtich to
use, I open them frequently. Plus, the electric control will close
them automatically if it rains. And it works really well, often the
first time I know it's starting to rain is the sound of the skylights
closing, as it only takes a few drops.
For install, I'd go with the advice to get a carpenter/contractor to do
it. I'm sure some roofers could do it, if they have the experience and
additional skills. But typically it requires some framing, drywall,
finish carpentry, and painting skills, which are different from what a
roofer normally does.