Welcome to the forum, Christina
First off, I would erase that 150 mile number from your memory, permanently.
Also, I wouldn't concern myself with any sort of buddy driving, unless you have a friend that is going to start driving as well, or possibly make a good friend while in orientation with a company. Even then, concentrate on getting your training first.
Due to a friend of mine who's brother is currently in training, I have learned quite a bit about Prime's training program, and judging by this guy's experience, it is working out pretty well. I believe he has to drive 60,000 miles total before he gets into his own truck. He got his permit, got hired, then got assigned to a trainer.
During his training to get his actual CDL, he drove something like 30,000 miles (not positive on the total miles, but he did a lot of driving). During this process, he drives ever mile that the truck moves, and the trainer is always in the passenger seat. At no time does the trainer drive the truck in regards obtaining miles. After this time period, he went back to Missouri and took him test to get his CDL. In his case, he was able to go back out with the same trainer (they got along well), and drive in a team operation for the remainder of his training.
Warning, they will push you to get into their lease program. Check it out carefully. I tried it years ago, and it was horrible as far as I was concerned. I hear it has changed.