It is indeed a bit naive, the wast majority of idols be it singers or gravure models make little to no money, only the really big ones can live off it (and Tomoe is not that big).Maybe I am naive, but I always imagine an idol as popular as Tomoe to be very well off financially.
As daredemonai said the smart ones finish high-school and then goes to university, not sure what plans Tomoe has but I'm guessing she just hopes to marry some rich guy.