Q:

Is there a limit on how many factions I can join?

Ok so I've been playing skyrim elder scrolls v and I am addicted. I know that if I become a vampire I can't become a werewolf. Is there any other restrictions on joining factions or a limit on how many factions I can join?

A:

There are no limit to the number of factions you can join, and you can join all the factions, bar Both the Stormcloak and the imperials, and the Dawnguard and the Clan. In each case you can join one or the other. 
Here is a list of joinable factions. Some factions can be invalidated by the following:

Greybeards: 

 Killing Paarthurnax

Dark Brotherhood:

  - Destroying the dark brotherhood

Imperial Legion: 

 Joining the stormcloaks

Stormcloaks: 

 - Joining the legion

Dawngaurd: 

 -Accepting the gift in "A new order"

Volkihar Clan: 

 -Rejecting the gift in "The new order"

These will invalidate joining these, so if you want to join the Dawngaurd:

 you have to refuse the gift.

