Alright, Here's what I *THINK* he wants.
If you want to have the priest created via life path, then here's what I think your friend should do. Apparently, there's a high path and a low path to this....it all depends on how generous the GM wishes to be. For the high path, the prospective priest can choose any stage 1 or 2 path he wants. Anything that makes getting into the University path painlessly should be a priority though. In my example, we'll use white collar and prep school. The prospective priest then takes the general studies path and really should end his University life there. He can then enter the Military Academy, take the Mechwarrior path and have enough to take one tour of duty. Anything more depends on if the GM uses the aging rules or not.
The low path is a bit cheaper, as the character will instead be taking trade school to represent a small seminary. Instead of entering a full fledged Military Academy, the character takes Family Training instead and has it represent one of the many smaller private military academies that dot the Innersphere. This method also has the advantage of being more open than the high path.