2007 F250 4xF and Horse towing

My mechanic is retiring and this will be the first vehicle I’m looking at a diesel to be my tow vehicle for bumper pull aluminum 3 horse trailer for So Cal. It’s a King Ranch Crew cab for horse show moms and kids. I last had a diesel dully in 97 and I was burned out on waiting for the engine to prime to start. It’s got 150K mileage and I’m never hoping to take it off road. I’m full of questions. Will being a 4x4 have any issues w just towing? How many miles should a Diesel engine go? What is bulletproofing ? This is from a horse trainers spouse that works at local Ford shop and he goes over the trucks. What should I be on the look out? Thanks so much in advance for you help.