Several things to think about to protect you.
1) Treat it as a purchase at this time, thus have a home inspection completed at this time and the Lease / Purcase contingent upon your satisfaction of the Home inspection. 1a) Make sure the home inspector is ASHI Certified and NAHI Ceritified.
2) Make sure you have firmly in writing what your payments go to, at times they can go to the principal and at times they go 100% to your lease only.
3) Make sure the earnest money disbursement in the end is spelled out properly as to what happens if and when one party does not perform.
4) You may want to have a preliminary Title Search completed at this time, This makes sure the current owner can sell the home at the end of the term of the lease.
5) A tough one is, What price are you going to pay at the end of the lease, The current todays agreed upon price which for the buyer would be the better way since homes are espected to rise in the next couple of years, thus buying at the 2012 price will be less than buying at the 2013 or 2014 price,
6) You should seek legal advise from an attorney if you feel the need, They will have many more ideas to contribute than the few above if you so desire. If not an attorney at least have a seasoned Real Estate Agent look over the contract.
Hope these ideas help, keep me in mind when buying or selling real estate,
Ralph Renninger CRS
Trust the best, a CRS