what's standard earnest money on a large mixed use property?

[Ashley Cooper]

I have a large tract of land that will likely be developed for mixed use. I was wondering what is standard for this kind of thing. Is it 1-3% of the purchase price? If the sale is conducted in parts and over a few years, does this affect the earnest? Also, is it customary to have a period of time before the earnest becomes non-refundable?

Thanks for any help!