It's what I'm running on my PCs.

Windows XP is no longer supported, and upgrading Vista to Win10 requires a clean install, and reinstalling all your programs and data.

You can get a program to check your system's Win 7 compatibility here. See what that tells you.

I don't know which version of Win7 would give you the smoothest upgrade path from Vista. If you're running 32 bit Vista, you'll probably want a 32-bit Win7.

I always buy a complete version, not an "upgrade only" version. A bit more expensive, but a lot more flexible.

I'm pretty sure you can get a version of OpenOffice that will run on any Windows version.