I dont know how complex your requirement is. But for just to sequently number documents while creating and saving them, is very easy. you need to create a profile document. Put a 0 as the starting value. Or if currently u have 100 docs, then put 100 in the profile document as the default value and then each time u r saving a document for the first time, change this value with +1 and add that value to your document and replace the value in profile document alos.
i hope only this is required. if iam not getting your requirement, then pls correct me