Vesta is an asteroid 530 kilometers in diameter. It will need to be hollowed out to create a terrarium.
Each one of Keri Bean’s 6,447 followers can have 8.22 hectares of land on the inside surface.
One year on Vesta lasts 1,326 Earth days.
One day on Vesta lasts 11 minutes.
That creates a centrifugal force of 2.35 gees on the interior.
Decrease the speed of rotation to 17 minutes for Earth-like gravity.