Nonrefundable deposit on lease to purchase option

Regarding nonrefundable deposit on lease option to purchase for a home selling for $375K.

What does the nonrefundable deposit entail?

1) For illustration purposes is it (10K) upfront that the seller gives back to the buyer? To assist with the bank required down 3.5%, 5% down payment?

2) Is there a portion of that nonrefundable deposit that is considered the cost for the lease option?

3) Do I charge seperate for a lease option in addition for nonrefundable deposit?

4) If lease is ending, and the buyer decides not to purchase home for whatever reason: Unable to obtain financing through lender, doesn't want home, change in job location, etc. does the buyer or seller keep that nonrefundable deposit?

5) If the seller wants to rent another year or so after current lease is up, do I apply another nonrefundable deposit. Or does it carry over?

6) Any knowledgeable real estate lawyers you can refer me to that can draw up this contract for me.