Decide what's important to MOST of your customers and communicate it clearly. Provide as much information as you can about your company and business. Convince them that you are real and not just a figment of cyberspace. Let them know how you can be reached in the real world. Posting testimonials on the site is also a very powerful way to establish a track record.
Customers expect a speedy response to email inquiries.
If you must hire someone in order to ensure a prompt response - do so. If you are not properly staffed you may diminish one of the strategic advantages of doing business on-line. When a customer sends you email, reply with an email confirmation and follow up with a phone call. Or - consider an email autoresponder for frequently asked questions. Be sure to identify it as such and offer another further contact so that the customer feels they have been personally serviced.