Stampduty registration on sale agreement and sale deed on property

1. When executing agreement to sale do We pay stampduty on whole consideration of property or the advance payment made? 2. Further when we execute sale deed do We pay the stampduty on outstanding amount or do We pay it all again for the entire consideration? 3. What if actual sale deed is to take place with a different buyer than the one in sale agreement (In case first buyer found a higher bidder n wants it to be sold to him enjoying the difference)? 4. Similarly what happens in case of registration charge in all the three scenarios? 5. Can the parties to sale agreement dishonour the agreement? Any remedies? 5. Does any of this get impacted when the land is agricultural land but within city limits? 6. Any reference to existing Acts and case law u can point to please?