You don't mention which B'mann mogul (the really tiny industrial one with the small, evenly spaced drivers, or the one that looks like this:
I'll assume you mean the one shown in the photo...
I've not measured the actual current draw of mine, but with 2 amp/hour batteries, I get around 2 to 3 hours per charge, which means it's drawing less than an amp with just the locomotive. (I don't have sound. With sound, I wouldn't expect that to draw too much more, so you're still probably in the range of 1 amp or so.
I wouldn't power the coach lights off the train batteries. I'd install separate batteries for those. With the baggage car, you'll have ample room--not that you'll need it.
Later,
K