DIYer here, researching the feasibility of installing my own kitchen
exhaust fan over a gas island cooktop.

I'm curious about connecting duct to a roof mounted fan on a pitched
roof. The sleeve on the fan is going to be entering the attic at an
angle. What's the best strategy to route the duct to meet the angle of
the sleeve? I can't put the fan directly over the opening. I have to go
over a couple of joists and higher up on the roof. Can I just come out
perpendicular from each opening with two short pieces of duct and an
adjustable elbow at the end, point the 2 elbows at each other and do a
straight run between them?

I'm going for the Fantech RE model. Any opinions there?

Where's the best place to put the backdraft damper? Seems to me near
the end of the run, close to the roof. This way there's less external
air in your duct.

Am I dumb thinking I can do this myself? A dedicated circuit is already
in place so it's just duct work and installing & wiring the fan. I'm
not seasoned handyman but have a good track record so far with
construction and minor electrical.
Thanks.