question about uninstalling and steam

yeah you can, but you have to "install" a game again and tell him in witch folder, you serch the right folder and steam can see "Oh ist already installed" then you can play not only that game but all games you installed in this folder

Yes, it should work. You may need to "Verify integrity of game cache" for each game.

i wont suggest doing that,its like putting a pirated game on the steamfolder-you may have problems.Just re-download

Yes, just backup your Steamapps folder and restore it after. Steam won't realise things are installed though, so install the games as usual, it will detect that everything's already there and will just change the game's status in your library to installed :)

I do this a lot since I have limited internal HDD space, so don't listen to the people saying it won't work

You should just use the steam backup tool. This will create a file that is fully compressed that you can then store on a backup drive or burn to disc that can be used to re-install the game at a later time. The one downside is that you need the space on your harddrive to create the backups but 99% of the time this isn't an issue.

Goto -> Steam -> Backup and Restore Games -> Check the games and go

It won't work for all games I'm afraid (Sacred 2 is the only one I can think of atm), but yes this generally does work and is a great way to save dozens of hours downloading (or in my case 100s). Remember to "Verify integrity of game cache" though before trying to play.

No!! not only SteamApps!

I recommend you to back up the userdata folder too. Many games store data and savegames there (like The Witcher 2), and you may regret it later. Happened to me before