steam games is easy to move, you just move the steam apps folder and when you fresh install steam you point out that folder and it verifies and uses that (you can restore it back to C if you use that in C)
i usually just go fresh.. i usually move everything out, including browser history saved games, the crap i have in my desktop
make an image of the HDD with macrium reflect in case i forget to move any special\leftover folder (i always forget to move some games that save the data in weird locations like appdata or programdata, saved my ass several times, although it wastes plenty of space.. but when i am confortable that i didn't forget to move anything i delete that old copy )
format, install the OS, and install the basic apps that i use like steam and firefox (restore the firefox profile\history. and point steam the location of the games)
then i try to only install stuff when i need it, i like to be minimalist