If Windows 8 came installed in your brand new computer then it should run fine. If you have a lower end one then in a year or so it may not be able to keep up with the game after all the updates and may slow it down then.
No reason why not - provided you have the correct driver(s) for the hardware installed in Windows 8.
Yes, I play Minecraft on my Windows 8.
No you have to buy it installed into the computer unlike windows which you can upgrade with a disc (I did when windows 8 came out).
You cannot get Windows 8 legally for free ! It comes pre-installed on new computers. Windows software - like most other programs is copyright material. downloading an illegal version just to get it free is theft !
Minecraft does not need to update for it to be compatible with Windows 8
I am currently playing Sim City 3000 on my Windows 7 computer, and it installed and plays perfectly, so the answer would be yes!
YES
I have windows 8 too. All you have to do is windows button+r then type in %appdata%
Yes
If you previously tried to download Windows Movie Maker for Windows 8, but it said that both the movie and photo programs were installed then you will not have to re-install. The easiest way to find it on your computer is to select the Windows logo on the left and type "Windows Movie Maker" (without quotes) into the search bar.
Windows 8 is commercial. You need to by a Windows 8 book.