I am not sure if CA law requires you to have E&O insurance, but it is a good idea. As a sole proprietor, all of your personal assets are at risk. More importantly, however, is the issue of a license and a bond. Many states require Credit Repair Organizations to be licensed and bonded in their state. This goes for every state in which you have clients. You should check with the state about that.
You need to check the state and national association requirements for your license. In addition many associations will help you obtain the licenses, bonds and insurance you need. As this is a hot topic area of the law I would want to be fully insured for handling others people financial affairs.