I use Windows 10 exclusively on the 2015 MacBook, I don't know how to use OSX and don't want to. I've had that combo running since May and it is perfect, couldn't be happier. No crashes, no hiccups, the new MacBook is simply the best ultralight for Windows ever made. To answer your questions:
Trackpad: Extremely accurate, zero issues.
Trackpad Gestures: These do not work natively but can work with a free add-on program that many of us use.
Version: Windows 10 is what you want as it's the only one compatible, and let me tell you as a Windows power user since 1995 that Windows 10 is fantastic, best and most stable version ever. You'll need to pay $120 for a copy from Microsoft, and as a bonus that version will be 'virgin' won't have any adware or free trialware on it. There are some in this forum who think the RMB runs Windows better than OSX if you can believe it, it's that good.
Like I said, I don't use OSX and don't want to so I have chosen to install Windows 10 via Boot Camp which is a free utility included with the MacBook. My RMB boots directly to Windows every time, it's like OSX isn't even there.
Feel free to ask questions, I can answer anything you've got concerns about.
BJ