Railroading is not for the faint of heart, particullary if you want to be in the cab of a locomotive. I'm not a railroad employee, but I was looking into doing it for some time and being an avid 'railfan' over the years, here's what I learned;
I don't know exact details of all railroads on how they operate, but I know CSX hires on Conductor trainees, you pay for training how many weeks then normally you get hired on when you graduate. You get field experience, yard work pushing cars around, uncoupling and coupling cars, throwing switches, and everythign else a train crewman does in the yard - learning the ropes of everything in real life situations, you'll also be gradually brought into a bigger scale of hauling freight, advancing to maybe industrial runs in the city you work, then going on long road trips.. with all this you'll eventually become a Conductor. There's lots of rules, and regulations. Safety is all railroads primary concern, and you can't slack off - one mistake and you might find yourself out of a job regardless of how little of a mistake you made. I guess most of the railroads require you to learn how to become an Engineer too, so you can be scheduled to do either. You'll be trained to learn how to operate the locomotive.
However, you won't be doing no 7-3 everyday. You work off an "extra board", you're basically on call 24/7. When you're needed, you'll be called and have an X amount of time to show up. Really, only the guys with a lot of times usually have the same schedule. You can also not work for days, I assume also. Basically to work for a Class 3 (CSX, BNSF, NS, etc. etc.) Railroad, you have to be for it all the way or not at all. Some railroad guys told me you have to really love the railroad to work in one. I believe you are subject to relocation at any time as well for the most part, but you are hired in a typical city to work out of.
13 hours I think is the max you can work onboard a train, then YOU have to have 8 hours off I believe, how do you get back home? Lots of different ways that I dont have exact details on, when you do crew changes you either take a ride back to your home city, railroad pays for a motel, or I think sometimes you may even ride another train back home.
Somethings to think about, you probably won't be home a lot, your body will have to make some serious changes to accomodate the sleep/rest changes along with working at any time of the day. Railroads are never off either, 24/7/365.
Im sure I missed a few things, I'm not trying to say not do it, but you'll have time to do plenty of homework. If you have a family, I'd consider looking at other options in the railroad other than train crew.