Trailering brings up another issue... If he's never really been away from Momma, AND has never been in a trailer, you may want to load her to come along for the trip. ;~D
Then put him in a strong place he can't break out of when she goes back down the driveway...
It would be nice if they would wean him from her beginning today while you prepare for his arrival.
VERY good advise!
Another thing you might want to do is to put him in a separate pasture or corral at first (if you have one), not by himself, but with one of your other horses, I think you said you had 3, who is the lowest in the pecking order. It's best if it's somewhere where they can all see each other but have a fence between them. That way he doesn't have 3 horses ganging up on him and beating him up (and they WILL) right off the bat. He can get accquainted with a less dominant horse first and kinda buddy up for a day or so, then turn them all out together. They'll still run and kick and posture at each other, but it won't be as bad and a whole lot less likely that any of them will get hurt or run through the fence.
When I first brought Bob out to be with Blade and Tennessee, I thought Blade was going to kill him. It shocked the heck out of me. Blade was just 2, but still a stallion. He was still making baby faces when Tennessee (16 yr old gelding) looked at him hard, but when I put Bob in there, it was WAR. They both ended up going over/through the fence. Luckily no one was hurt and I caught them both before they made it out to the road. I took Bob back to his mom right then and didn't bring him back until after I had Blade gelded and taken to the trainer's. That way Bob and Tennessee had a month to get to know each other and Bob had time to get used to being without his mom before Blade came back. It was kinda funny though when Blade came back because it seemed paybacks were in order. Bob ran HIM all over the pasture and tried to mount him like he was a girl. They finally settled down after about an hour. So, it can be a tricky time, just be careful.