Pick someone who has both business (service industry) and cyber-law knowledge. You're running a business, you're providing a recurring service, you're making promises about what you will and won't provide and setting rules on how your clients can make use of the service. That's a legal contract. You'll need to know someone who can advise you of any pitfalls, or be there to back you up in the event that a client begins to cause real problems for you or your business.

Just remember: you don't have to keep this person on retainer. You just need to know a reliable resource to call when you have questions. It can also be a good idea to have a legal professional read over your TOS and advise you of any potential pitfalls, for either you or your clients.

Use your local bar association as a primary point of contact. They will have a list of specialists in your area, and can make some initial recommendations for someone local.