Pc games reinstall!

i want to do fresh install of win 7 but i got pc games on steam do i uninstall them first and then reinstall win 7 or just format everything at once also will i be able to download the games again with all the dlc because i bought black ops physical version and and bought all the dlc for it,so would i have to use the disk again and then dload the dlc again.the rest of the games were bought digitally from steam (mw2+1dlc,l4d2,plants vs zombies,gta vice city,sonic and sega racing)and some f2p games.other physical games cod5,bf3,bfbc2.i dont have anyway of backing up all my steam games.i also want to know if steam saves all the single player campaign saves/gameplay settings and configurations