Any lease need to be logged at the land registry to be legal! I do not know if an "intent to lease" can be registered at the land office so I do not think it would have any validity!
You cannot make any agreement which looks like you assert control on the property as this is in violation of Thai Constitutional law and will overturn any agreement to the contrary!
Buying a house with land in Thailand is not possible as a Farang cannot hold land in his name there are 2 work arounds 1) Lease the land for 30 years ( I believe) many will tell you that you can lease for 90 years I suspect that there is danger going down this route, you pay your money you take your chance! 2)Set up a company and put the title in a company name. To do this you need Thai shareholders to act as nominee shareholders! Acting or requesting some one to act as a nominee (or straw man) is very illegal! Up till now the powers that be have turned a blind eye! We have had a change of government here to a populist one! They are proposing now to tax Farangs on overseas income, this is a big change if it happens. They might crack down on other things! Your choice, your money, but do remember using a company is not legal up till now its tolerated!
I have heard similar in other countries! The issue for the Thais is what if your tenant defaults on his rent and you do not receive the money you state that you will receive! Annuity backed pensions are guaranteed to be paid whilst other investment income is not! This seems to be a new requirement, there are many!