no steam retail codes cant be reused
no you cant steam friends in an acount.
no
You Can't I'm Sorry :(
You create a steam account and download the steam app
yes
No, it is not possible to play Dota 2 without Steam. Dota 2 is exclusively available on the Steam platform, which serves as its distribution and matchmaking system. To play the game, you must have a Steam account and download the client.
Yes, but it must be purchased as a gift for someone. You must have their email or steam account. You cannot transfer a copy that belongs to you. Only one that you have bought to gift to someone.
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?
No, unless you let them on your account, which is a bad idea and not recommended.
No, once a game is added to an account, it is non-transferable. The only way to transfer the game at that point would be to give the whole account.
Through steam pipes.
You should be able to, as the purchase will be linked to your steam account, not to the computer you were on.