My experience when I started working on the plains was a lot of near death experiences. My advice would be:
A) Find a rock that enemies can't climb up and set up a portal to your main camp.

B) Scout out a border area with a forest or meadow to set up your permanent plains camp, then dig a deep nasty hole for everything to fall into while it is attack your fledgling castle.

C) When building your plains base elevate soil in your catch pit, this way your castle is safe, and always build in stone on the plains. A fenced in and elevated field is your friend. Since plains crops only grow on the plains you have little choice, but a 2 or 3 high stone wall system will often mask your presence from deathsquitos.

D) Create a set of stairs into your catch pit and lead some lox down there for taming. By far some of the best meat farming in the game, but hard to start. Once the lox are in the pit go through your taming process with barley, cloudberries or flax. When you get so many that your food is disappearing right quick its time to get your butcher knife out and put it down to 4 or 5. (Be mindful of deathsquitos though, they kill lox babies.)

Having your deep pit moat really is key in the plains, once your guard lox are tamed there isn't much that can harm your base.