In addition to the other guy who answered you: Technically you don't necessarily have to reformat you hard drive to install Linux. Many installers give you the option to resize an existing drive and install Linux alongside windows.

Also according your steam library: As far as I remember you can export and import single games and you may be able to move your steamapps directory to your Linux installation but this may or may not work depending on your setup and your games. If you don't have a limited Internet connection I would recommend just re downloading the games your planning to play.

Cloud saves work fine whether on Windows or Linux.