Yes I know what you mean. I've also been looking into duel careers, not quite sure how I'll juggle everything but I'm sure I'll figure it out. Here' s a good story about someone who's doing it all:https://www.news.utoronto.ca/bin6/041231-818.asp
Inasmuch as one considers a career meaning that one makes a living at it, Charles Ives had only one career, Insurance (founder of New York Life I believe). He composed as a hobby and generally paid people to play his works and rented his own venues. He made enough money in his job to do whatever he wanted with his art. Almost the perfect combination.
you can't manage two careers at the same time too long (i mean 2 careers, not 1 and a hobby). you can juggle for a few years, but then you have to decide what you really want - play the piano or make money
It depends what you want to do. If you want to be a travelling concert pianist, for half a year then the other half your other job, you might get a little stuck. Because of the study required to maintain repertiore and standard of peformance is rather high if you dont want to be regarded as a hack.