You can never be signed up with too many companies because even those who have no client in your area at the moment may get a client for 2020. Similarly, a company may have a couple of 'go to' shoppers in your area who quickly snag all the work such that you see nothing on the job board that would indicate there is work in your area. At any time those shoppers may move, quit shopping or have a falling out with the company such that the jobs suddenly are available.
The best advice I can give you is to sign up with the companies at the top of our list and then over time sign up with the rest of them a few at a time