This probably belongs in the NFA forum.
The receiver is what will need to be registered if you want to build an SBR. And you'll need that Form 1 stamped and returned to you before you can assemble the gun.
You can do a trust if you want. It's a preferred method for NFA nowadays, as it allows you to set other primary owners of the gun, and who it would be given to, should something happen to you.
But adding friends to a trust is not a good idea, IMO. That makes them equal owners of the gun. If it's just you on the trust, they can still shoot it, as long as you are there. Personally, I wouldn't hand an NFA device over to a friend for them to go shoot without me accompanying them, anyways. It's an investment, do you want to leave it to someone else's discretion?