1 you can enter into MOU or agreement for sale .
2) the detailed terms and conditions as to the price to be paid for purchase of site , time for making payment , receipt of earnest money should be incorporated in agreement
3) it should also mention consequences in case full payment is not made within stipulated period .
4) get MOU or agreement drafted by local lawyer .
5) seller wont issue any POA to you as only advance payment has been made till date