1 -> Yes, Ubuntu installs a bootloader.
2 -> There are winsimulators, but don't expect too much from them, modern games will not (or barely) run on those.
Dosbox works in it, and there are several emus for other (older) systems.
3 -> see 2, if your PC is meant mainly as gaming rig you don't need Linux. Otherwise you can do all that you can do in Windows.
Advantage: all is free. (OpenOffice-Gimp-Whatevers Whatnots.)
More info if needed:
http://www.ubuntu.com/