A very good question, with many long, complex answers.
As a starting point, take a look at flippa offerings to get an idea of common metrics disclosures.
You can also search for flippa + metrics + read up on the entire deal flow of site sales.
In general, most sites sell for 2.5x-7x yearly profit.
This also depends on payment spread. In other words, a site might sell for 2.5x cash or 7x paid a 25% of monthly profits, till sale price is reached.
If you go the 2nd route, be sure you escrow your DNS records with an attorney + have a reversion clause.
In other words, if 3 years into the deal, the person you sold to gets hit by a bus + can no longer make payments, then business reverts to you, along with control of DNS records.
Very important to have a reversion clause which triggers any time your buyer fails to make a payment.
Many people miss considering this when they sell a business for payments over time.
Which is tough, because many times you can sell your business for much more money if you're willing to sell over time, rather than a single up front payment.