hey question above 
No, use the download link for the launcher on the website (not forum) profile page.
Later you will get a Steam code for final.
How in the world you want to play game on Steam that has no early access there and is not yet released.
There is a Steam forum for the Beta for the (mostly higher tier/alpha) backers who have codes for that version. The majority of users are accessing the beta via the launcher though.
When you buy this game via homepage you will get a steamkey, at release, for the full game.
Yes, if you have a digital version, you will get a Steam key at release