Yes. You will likely want to order new templates/stickers, t-nuts, and ptex disks, but you should be able to get these individually from voile without buying a whole new kit.You'll need new rivets for the tip/tail clips as well.

It depends what kind of riding you're doing with your dh, as that's a pretty good board for all different stuff. This is a stiff binding, so if you're riding steep lines and dropping cliffs then I'd say yes. If you're building jumps in the backcountry or riding all around I'd say maybe. If you're riding park I'd say no way jose.
I had some flow nxt at bindings and I liked them but they aren't very responsive. I like ride binders better now.

I would go medium. However you could make a large work, they would just be bigger and heavier than necessary.

m/l should do just fine

^ don't change your binding size based on your board size. boot length is all that really matters (and width kind of). But if you're rockin 10+ boots get large, no question.

large.

I hate it when bindings are on the small side. It sucks when you have more toe off the board than heel. Also, you want the footbed to reach all the way out to your toe so you have good responsiveness. I wear 10.5 boots and always ride large binders. I have some M/L Rides and I wish they were bigger.

I'm thinking that might be a bad idea. i had a burton supermodel i was about to cut but the insert pattern would have made it a pain in the ass. the problem is, even if you have a burly enough saw, once you cut the inserts in half, they'll start to pull out and cause problems. i split a forum instead, i just think keeping a saw away from burtons is a good idea.

I'm thinking that might be a bad idea. i had a burton supermodel i was about to cut but the insert pattern would have made it a pain in the ass. the problem is, even if you have a burly enough saw, once you cut the inserts in half, they'll start to pull out and cause problems. i split a forum instead, i just think keeping a saw away from burtons is a good idea.

I have a slightly narrow foot, and have a bit of wiggle room, but it doesn't bother me. I would say these would be a great fit for someone with a normal or slightly wide foot. If you have very narrow feet I might try a different model.

I ride the K2 Believer 157. I absolutely love it and would highly recommend it. However, I believe dogfunk is all out of the 157 size.
Get the 159 if ya like pow, get the 154 if you like park. or if you really want a midsized board, find the Believer somewhere else or look at the RideDH or the Lib T.Rice 157. Good luck!