I have a little advice copying files in steam. Install steam first, then move games into the files they should be, and steam will auto detect them so you don't have to re download it all. Steam also can set up a folder on every drive on your pc and has an interface to move install folders between those drives, but i don't think steam likes adding a folder filled with games to the file system, so just make a new folder and drag and drop. When I moved from non-steam to steam, I just copied all my maps over and they come up just fine in game, no re downloading and they show up fine in the in game map browser.