I think we can look at Carlson Wentz as a good reference of what could go well and what could go wrong here in this situation. Although he didn't come from a big school running a pro style offense, he started right off the bat and caused a good impression, he's had a good first couple years and in general, with a feel different circumstances we could be talking now about a SB champion and maybe a QB in a different tear, instead, when things start to go wrong some of this guys can derail really fast.
One aspect of Brady no one talks about is his mental strength, I have seen very few athletes on that level, and it's not by coincidence they win so much and are the goats, I can think of Brady, Jordan, Rafael Nadal, Ayrton Senna. In Brady's case if he didn't have that factor, he could very well stopped at 3 rings and be retired for quite some time. I'm mentioning that because I don't think we can expect even 40% of that from any of those young dudes. Brady is an old guy raised in a different society with different standards and that translates to accountability and many other things.
The Eagles didn't screw him up like the Colts did with Luck and many other examples but they had some management problems, QB controversy, players talking too much and even Carlson, at some point someone should have put him in his place. Problems I don't think we can worry about in a Patriots environment with BB running the ship.
Mac is in a perfect situation, he doesn't need to carry the team, just be a game manager and do not screw up while he develops to become a franchise QB some years from now. I think we got very luck with this draft.