Business Law/Legality Question (Letter of Intent)

Hello, I am not a lawyer but I would think there are one or two on this messageboard. I have a music booking agency in New York, Westchester County (based) and need to develop 2 Letters of Intent (LOI).

The first LOI will be used to solidify a specific date from a particular venue. Meaning, we are booking a tour across the Northeast. We are contacting venues with all of the information and once we have a venue interested, we want them to sign our LOI. This LOI will guarantee us that they will reserve the space/time/etc for us on the day we agree upon. A contract will follow. We need to add one clause in this LOI, as we have not solidified our headliner as of 'yet'. Our headliner is going to be a fairly large band that will draw some big crowds. The venue will have a clause in the LOI that if they do not like the headliner, they can withdraw from the LOI up to 3 weeks before we arrive at the venue. This protects the venue.

The second LOI will be used to get serious communications established between our company and a particular band. We do not add to our artist roster every band that comes to us, maybe 1 out of every 300/400. So, we need LOI's from bands who are serious that they want to go into further discussions with our company about booking, etc. The LOI will keep them focused and serious, and not looking elsewhere for particular booking for a period of time, until we agree on terms and sign a contract.

My question here is:
What exactly needs to be stated in a LOI? What are the 'terms'? I have signed many LOI's regarding "Sale of Business", but not for the entertainment world. Any ideas?

Thank you,
Darren Herman