If I were you, I would do the following:
1) Find a stable day job that covers your bills.
2) Devote your nights and weekends to finding billboard locations and/or other outdoor media opportunities [your "night job"]
3) Buy my new updated book and CDs that goes on sale in about two weeks, and read and listen to them 10 tiimes until you have 100% understanding of the strategies and tactics.
4) Come to my Boot Camp next week, if it meets your schedule. It will speed you up on your learning curve by 1000%.
5) Keep working both your day and night job until your night job fills up your day hours and covers your bills.
This is how most successful people in the outdoor business begin. You will actually hurt yourself by working for another billboard company as a day job -- the conflict of interest will preclude your "night job", and potentially get you in a lot of trouble.