only the spellbooks really in my opinion the rest are worthless but theres probably a reason for them if they exist
no there is no books on previous adventures of the characters from Skyrim elder scrolls.
No
yes,i need
yes you idiot what do you think
You don't need to buy Skyrim from Steam, but it does need to be linked to your Steam account (by registering the serial code you should have got with the game).
Usually, to get married in Skyrim, you will need to do a quest for the person you are trying to marry.
They are used for when you do side quest for one of the Thieves guild member.
I think it´s skyrim!
It should tell you if you need to update
Not necessarily. You might need it to instal it, if you don't have the disk along with Skyrim when you bought it. But once it's installed, you can play offline same as you can play regular Skyrim offline.
Dawnguard is basically an expansion pack for skyrim. like all expansion packs, it requires the base game to play. So on a PC (and any other gaming device) you need skyrim first and then you can install dawnguard.
If you need a claw to open it, check to palm of the claw in your inventory. If not, look it up on cheatcodecentral.com or any Skyrim forum.