Definitely need one, may need them all. I presume the transition is to allow connecting the hood to your ducting and would depend on the size of the hood's exhaust collar and the size of your ducting. If they are both 10'' (and with 1200 cfm they should be) then I don't think a transition is needed.

Wall cap? Not so sure, I'd have to see it, but if the penetration of the duct into your ceiling is concealed by a faux chimney I don't think it would be needed.

Backdraft damper--definitely!! Otherwise every time the wind blows outside you'll get a cold blast down into the kitchen through the hood.

Thanks so much!

Backdraft damper- yes

Transition - depends on whether you need to convert from round to rectangular or vice versa, and that depends on the product itself. Look at its PDF on the manufacturer's web site. Then see whether you can use that exit duct as the shape (round or ractangular) as your purchased duct taking air outdoors.

-david