Yes.
Tunngle for LAN or Phoenix (to install and play single player steam games) still looking into tournament MP.
I purchased Portal 2 but accidently assigned the steam account to my sister's PSN account rather then mine. How, if possible, could I re-assign my steam account to my PSN account?
Yes it is possible if they are put into different folders on your hard drive. I have Shogun, Medieval and Rome including their expansion packs of Viking Invasion (for Medieval and Barbarian for Rome) on hard drive as well as both Empire and Napoleon Total Wars on my Steam account. All play perfectly well.
To create a Steam account you need to go the the Steam Powered website and go to Create A New Account. There will be a form to fill out and you'll get an email with a verification link that you need to click.
Yes, but it's free.
no you cant steam friends in an acount.
Yes, you need a Steam account to purchase and play Garry's Mod (GMod). The game is available exclusively on the Steam platform, where you can buy, download, and manage it. Additionally, having a Steam account allows you to access community features, mods, and multiplayer gameplay.
It is not possible to delete a Steam account. However, you may be able to contact Valve (the company behind Steam) and see what they can do. Contact link in the related links below.
No, Just Cause 2 does not require Steam. It can be bought on a disk for various consoles, including the PC.
Yes but games are not
yes
The lower the digit count the older the account is.