The simple answer is: yes
The were you to join construction strikes me as a little formal/old-fashioned, but is still acceptable.
Slightly less stuffy would be: If you were to join.
I suspect that most people today would say: If you joined.
If you would join is also possible. For some AmE speakers this is a simple alternative to: If you joined. For others, and for many BrE speakers, this construction would imply: If you were willing to join.
In your second example, the would you be construction is possible only if you are asking a question - and you therefore need a question mark at the end of the written version.