How to automatically populate the contract number in the field sales document number in IW52

I am implementing SD module for our client.We don't want to go for a much of customization at this moment as scope of SD is very less.Client has a requirement that before inquiry there should be a step for sales requisition from where requirement for material and qnty to be sold will be raised from plant to Corporate HQ.This should be the first step for any sales process.What I have thought about is that creating a service notification through IW51 and putting this number in the reference field in the follow on documents manually so that there is a link as there is no provision to create an inquiry from notification in std.The process should be Notification->Inquiry->Quotation->Contract->Sales Order->Outb. delivery->Billing.

What client wants is that the contract number should get automatically populated in the sales document field in the IW51 screen once contract is created and this should automatically close the notification i.e status should be Completed.As I am new to this module I don't know how to implement this.Gurus Pls help.