Expenses management is of course essential. But only one income stream? Three core activities - drink, food, accommodation (depending on the premises). Plus a range of other options within those - events, outside catering, functions etc etc. All with risks, regulations and challenges of course, but you are asking the right questions in the right place.
As suggested above, a few days, weeks or months work experience while picking the brains of your employer/host/mentor and observing everything would be invaluable.
Even if you ultimately want a Free House, the pubcos and breweries have lots of information on what they want from a manager/tenant as well - might as well build up that list of required skills as you plan your research and training...