I believe it is very difficult to transport boars from one landmass to another. Not impossible but might not be worth the trouble. maybe secure the boars in a safe breeding shelter on original landmass and portal to cull them every now and then.
Breeding a 2 star boar with a non star boar has a chance to produce a 2 star boar. Best practice is to remove the no star when a 2 star boar is produced so you have two 2 star boars to breed.