You can choose to rely on platforms where there will be clients waiting, but you'll have to make a decent portfolio even there. I don't think hiring an agency would be the best choice when you're only starting. It'll be a loss if you pay for it and get no clients in return.
Oh! Tough market! I don't live in CA, but I know the competition there is pretty high. If you can afford it, why not? I think advertising your business is an excellent way to attract potential customers quickly.