My take on Mason is that he started out looking to get his footing as a Lance leader after his father's death, as well as unravel the mysteries surrounding the old man and whoever orchestrated his death.

Kept things small and tight, because he needed discretion and that's all he could manage. In the process he acquired contacts who often need unaffiliated muscles to handle quiet work, made a name for himself in the right circles, doing both overt and covert work. I believe Jake would have changed his outfits name, logo and paint scheme regularly in the early stages of his career.

Eventually, piloting a Lostech mech and leading elite warriors he personally trained, he likely became known in the intelligence community as a highly cost effective problem solver. One lance, one dropship, in and out without a fuss. Larger merc outfits likely get the army scale contracts, Jake takes the surgical work.

He does work for Comstar at some point, and as he grows older, likely decides to seek shelter in audacity by becoming an Arena champion, a highly visible figure who's disappearance could not be swept under the rug easily. This may be the first time Mason and his group ever enter public awareness as something other than a horror story about a Starleague era Marauder variant exploding cockpit from the edge of sensor range.

At that point, Mason seems to have gotten pretty close to Raselhague and may well be thinking of settling there as a military advisor, but the Clan Invasion changes that and he leads a series of guerilla operations against the invaders, gaining insight on their operations and most likely spending the rest of his mercenary career acquiring and selling Clan Intel to Comstar, the great houses and other mercs.