I didn't have to move anything, not 100% sure of Deuce windshield, but I have a mid that goes up just to face height. Cuts the wind, I just prefer not to have it on most of the time due to looks. And yet I still have my sissy bar on back for passengers.. I like it with as little as possible.
Yes you will need to lower them. You can either drop them down with some extension arms, or remount them with some universal fork leg clamps. I think Kuryakyn makes the clamps.
Yes you have to slide the signals down a few inches with the Classic Deuce. Memphis Shades sell a nice signal relocator kit that mounts them to the forks, simple to install.....I've run M/M 'Deuces' for years and like them.