My dad, now dead, took the Modern Gun School courses by correspondence, and turned into a fairly proficient gunsmith in his retirement years. (There was a pawnshop, nearby, and he ended up doing all their work.)
That said, I read a lot of the MGS materials, and while good, you needed to have the right mind set and abilities before you started that course. With the right background and experience, I think they would be helpful. He had them -- he was a life-long do-it-yourselfer, jack of all trades, and journeyman mechanic. I'm almost the same way, but lacking in some regards -- I don't think I have the requisite patience.
As for the question about Mechanics and certifications -- going with an ASE-certified mechanic makes, sense, but Ive had some 'certified" mechancis do some ugly things to my cars, while a couple of non-cetified mechanics have done wonders.
One of the best gunsmiths I know was self-taught, another did an appreneticeship with an experienced smith. A few started out as police armorers. I know only one who has gone through FORMAL gunsmith training at a school.
The biggest issue, I think, is where they get their metal-working experience. If there's a good technical college nearby, with metal-working machinist courses, that's a good preliminary.