If you form a corporation, yes, you do. You will also need this number to register with a clearinghouse. You can contact the Feds for the correct form to use. There is no charge for this. You should take out a simple policy that covers your computer equipment and the like.
Some homeowners insurance covers office equipment up to a certain limit.
As for liability insurance you will need to decide this with your insurance agent. In our contract we list that we are not going to be held liable for clerical errors. By doing so you should not be responsible for errors and omissions. You should seek the advise of a competent attorney. You can contact the National Association of Claims Assistance Professionals, or the International Billing Association for policy information.