Scott
Firstly, if you want to sell then you should make contact with the solicitor. Then you should insist on a confidendiality undertaking BEFORE giving any information regarding your business.
If it was me, then I would be putting a valuation on my business, not anyone else so speak to your accountant, he will be able to help with this, I work on the general rule that the business is worth 50% of its annual turnover.
Final tip, It is normal practice for the purchaser to pay your legal fees.
Hope this helps
Chris