if you do a search for quilted duvet's you will find a number of tutorials - there are a couple books/patterns on the market for them too- they were quite popular a few years ago. your ideas sound about right-
as for binding- since you plan to sew it pillowcase style to make the duvet cover you do not have to worry about binding. you can always topstitch around the sides after constructing/turning right side out if you wanted to.
as for quilting- since you are not using batting that requires quilting stitches to be a certain distance apart you can quilt it any way you want that works for you & your design...a little or a lot is a personal choice when batting is not a factor. they are normally quilted to a backing- then constructed into the (pillow case) with a flap to fold over with buttons, zipper, velcro, what ever way you want to finish/close the top. show us pictures when you get yours done- we love looking at new creative projects.