I am considering moving my computer from Windows to Steam OS. If I do, will i have to reinstall all of my games to then play them on Steam OS? Thanks.
Yes. SteamOS is built on top of Linux rather than Windows, so a download of the correct version of any Steam software would be required.
Yes, As previously stated SteamOS is built on Linux and would require the Linux version of the game, but given your question you may want to check how many of your games have Linux versions, moving over to SteamOS could limit which games you could install and run. Unless you are using a program such as WINE.