Why would you want to Lease land for 20 years--- it really doesn't make a lot of sense .
If you are thinking of building something on that land to live in--then give it back to the owner after 20 years ,
leaving the woman you will probably meet and live with nothing---then it makes even less sense.
If you have not live full time in Thailand before , then yes rent --
--- have a look around for a few years, maybe by then Vietnam, Cambodia, PI, --might interest you more.