I worked more than 10 years in a dealership, worked my way from the bottom helper guy up to one of the top techs. I started w/ a 3 drawer because I got it free from autotech in high school and I knew I was going to be shop b*&%h for a while so it didn't matter if I had tools. I bought a craftsman 41" ball bearing and lived with it my entire time in the dealership because after about 4-5 years I knew I wanted out. I had to invest in a roll cart, and realistically, did all my work out of the roll cart. I got the huge Matco cart with a work table and all that (off craigslist very cheap).
My advice is save money on the box. Craigslist has many great deals. If you feel strongly that you'll be wrenching more than 5 years, a box is probably worth the investment, but I still wouldn't buy new. Buy it from someone retiring or giving up on wrenching off the internet. Buy a repo or trade in.
Or (and I am in no way affiliated) buy one from Strictly toolboxes. Google them. I told my friend about them that I used to work with, but like I said, I never had the intentions of staying so I never wanted to invest in a big box. He got a 72" from Strictly and its great. After seeing it in person and hearing about their customer service to him, I'd never consider anything else (if I was shopping new). The quality is great if you can find a box they sell that you agree with.
Now I'm a government fleet tech, and my advice to you would be get into some sort of fleet, salaried work if you can. And remember to shop for a box that you'll be able to keep at home if need-be. I don't think everyone can fit a 72" box at home, but a 52" should be do-able in most garages or sheds.
And I read somewhere in other posts, Matco trucks are few and far between. I've experienced that as well. In a very busy district, our tool men were always vanishing except for snap-on. I had a great matco guy for 3-4 years, then never again in my 12 years there. Mac was off and on each year it seemed like, and Snap-on was always there.