Dear Vishwas ,
As per your scenario you given requirement , but you did explain how you want input to map in SAP .
As per my understanding I will give some inputs which will useful for you process.
1. create sales contract in VA41 with item category WVN , here it is AMC service so there is no delivery , you can map with reference to sales contract create billing with F2 .
2. here it is fixed for 5 years with 500000 , so check the dependence how you will maintain price ,type of condition, some routine for calculating the amount in alternative calculation base value ..etc....
please let me know for further inputs .
Regards,