Mostly open with some trees. Wild grasses. No shrubs. We each have 14 acres on the end with 20 acres of community pasture between us. They want to rotate 4 pastures. This is all new to me. The horses on about an acre now.
It's hard for me to evaluate the grass from here, probably even if you took pictures... If it's drying out and has gone to seed, no worries.
If it's a lot lusher than what they are used to, they might be at risk of foundering to be put on it 24/7. If it's tall, it might be good to have it mowed by a brush hogger before they get there. What you don't want is for them to be able to sit and grab big mouthfuls of green grass at every step. If they have to walk around and nibble to get a mouthful, they'll be better off.
It's always good to fence off a smaller paddock they can be put in when you do the other fencing... and it probably wouldn't hurt to put them in that at night and feed them a bland hay before turning them out. When my pasture is borderline too lush, I feed them a bland hay to kindof fill them up before they go out. Then they are just grazing to stay buzy, they aren't gorging on it because they are hungry.
But all my advice is from experience with Northwest grass.... if the other Texans say don't worry, I'd trust them more than me.