The money isn't locked away in a Roth. You will always ha e access to your *contributions*, but not the gains. Also, I'm assuming you are in a stupid low place tax-wise right now a d I would assume that doing a Roth is the exact right place for your money.
That being said, the most important thing to do is start investing and stick with it. The details of what fund, where to optimize, what type of account, what tax benefits, etc are less important. Once you get started you can decide to optimize your knowledge later. The key is to invest in low fee funds and stick with it.
Also, my DH is a ME and works for an oil services company. His pay has doubled since he graduated in 06. He works 60-70hrs a week and has a very stressful job. Manufacturing is just that way. Plants operate 24/7, so engineers end up working long hours.tl;dr- manufacturing engineering will give you both the desire and salary to retire early.