When they call or write, you can take it from there and see what their specific needs are. A good brochure will pay for itself many times over. It is very important that all proposals be in writing. A proposal or contract which is written will help define exactly what you are expected to perform for your client. It should include dates regarding deadlines and how payment will be made.
Fees vary according to the industry or situation.
Some consultants prefer to work on a monthly or yearly retainer basis for their clients. Others like per project fees for work done as formulated in their contract. Your attorney could help you develop a contract form which you are comfortable with in your business. When you begin any business venture, you should confer with a trusted attorney and accountant. Your circumstances are unique.