I wouldn't count on lots of overtime in either your personal or financial planning. That is a huge variable, depending upon where you work, down to the shop level. I hired in here in I&C, and the shop OT policies for new guys was different than the other crafts (Electricians/Mechanics). They took the guy with the most OT hours, added one, and assigned us that many hours when we came in. Generally, except for job continuity, when OT is given out, it is offered first to the guys who've worked it the least. Since us new guys were hired in with several thousand hours of OT to our credit, I figured it would have taken about 7 years before I would be offered OT. (And no, it isn't reset on a year to year basis) I had job continuity OT several times, and everyone gets a chance at package walkdowns prior to outages, but in my 3 years in I&C, OT was pretty negligible.
As for Ops, things are going to change, as has been mentioned previously due to the FFD rule changes. The rotating schedule certainly has a small amount of OT built in, but filling in for other crews on relief week is going to be curtailed a bit.
But, let me chime in... After working 3 section Enterprise in the yards, standing 24 hr PPWO, and then a regular work day following that... Falling asleep at red lights on the way home... Well, even when I was on 6 section rotation in the best of times... Commercial power has allowed me a ton more time off!! (Until I started License class, but that's another story)