Hmm, I wonder how big my Steam folder is. Fortunately I bought a 1TB additional hard disk for my computer a year ago, and decided to stick my Steam folder on there. So now I'm a little bit less worried about reinstalling Windows...

I thought to try this the last time I reinstalled Windows and Steam... didn't like it. To put it mildly. I ended up having to download everything again.

I remember I found a tutorial somewhere about how to change the location of the Steam apps folder and it worked without any problems. I think all you needed was the exe file and the apps folder in your new folder, and by clicking the exe Steam would re-download and install itself in the new location.

The real bummer is tracking down all the various save files all over the hard disk...

If you haven't already pulled the trigger, this procedure worked for me when I moved the installation to my other hard disk:
https://support.steampowered.com/kb_article.php?p_faqid=231