Hi Rishika,
I think ORDER PRP_I object is also obsolete. The POD linkage in CRM 7 is from table CRMD_ISUEXTA4.
Call CRM_ORDER_MAINTAIN to create header , items , dates, partners, products.
You may need to create business agreement as well if not created already and set it on item.
To add POD call method CL_CRM_ISU_ORDER_CHANGE=>SET_POD using ITEM GUID and POD GUID.
To add business agreement call method CL_CRM_ISU_ORDER_CHANGE=>SET_BUAG using ITEM GUID and BUSINESS AGREEMENT ID or GUID.
The classes CL_CRM_IU_PR_CNTR_START_HD or CL_CRM_IU_PR_CNTR_START are for utilities Process Framework and used in UI. You cannot use those classes to create contract but you can have a look at them to refer the data is being set.
Regards,
Naresh