My Dear Friend Hari,
I would like to make it very much clear that according to section-17 of Indian Registration Act, 1908 when in a document a right, title and interest in an immovable property is trasfrered from one hand to other, the document becomes compulsorily registrable, therefore your agreement does not require registration. It is valid if it is signed by both the parties as well as two attesting witnesses. So far as the money is concerned you can forfeit it if your agreement contains any agreed provision for that.