If you have silver armor and poision resistance potion + best boat, you can land in swamp no problem. Its a good idea to find some already build castles on a coast of swamp and put a portal there.

Then you move to plains, look for a good place to set up, place down workbenches (and wood araund them) and start making a ditch araund your base to prevent furlings from entering your new base.

Or just do this next to plains lol:
https://i.ibb.co/bK3xvhM/20211205155301-1.jpg