Will Blender still work on Windows 10, and if so, will the full screen functionality still work? Are there any issues with Blender and Windows 10 I should be aware of before upgrading?
As far as we know right now, no, there won't be any issues.
Windows probably couldn't afford a major change in their programming API that effect Blender.
It would probably make a few large software companies a bit angry.
As far as the fullscreen functionality, this is something that shouldn't really be effected much by the platform. If it wasn't working on a specific platform (that Blender can run on), it would be a major bug. Lot's of people (including myself) use this all the time to help focus on our work a bit more, and loosing the functionality would probably make half the community extremely angry.
Just a disclaimer, I haven't tried Windows 10, so I can't say for sure that Blender won't work on it, but I am extremely confident that it will.
I have W10 Pro (build 10240) Blender 2.76 (2015-10-11)
Running multiple instance of Blender 24 hours a day for 1 month. Blender hasn't crashed
Full screen functionality.. not sure what that is. If it is where you CTRL right arrow to change the screen windows, yes can see the 3D view full screen and also drag new windows into it to see multiple views)
(Can pan with middle wheel click.)