If you do a vac form itll have to be a multi piece. That means youll probably have to cut your sculpture up. or, make a solid cast of yoru sculpture and then cut that up.
Either fett pride, or boba maker just made a tutorial showing how they cast their boba helmet. Two piece front and back, with locking mechanism.
Im right where you are at the moment, I understand how some of this works, finally, but dont know where to start