I'm think I'm on the way to find the solution, but I need some help at a start.

I'm planning to create a Main Line Item Database, that would have at least 5 child files (Quote Line Item, CustOrder l.i.,Order l.i., Deliveries l.i., Invoices l.i.) linked to their relatives Databases (Quote Db, CustOrder Db,...).

A Unique ID will then be adressed to each file that would have same Quote N

No, lookup brings related data back into the main file.

You need a script to make the new file. Scripting the process will be easy: integrating it into the interface will be the challenge.

Do you know if the doscript plug-in could be used here to automate the creation of a record in my Main Line Item File as soon as a new record is created in the CustOrder Line Item File.

I would therefore set this kind of automation :

1. Traditional Script in Customer Db called "New Customer Order" :

External Script - CustOrder Line Item Db - Count current number of records:: define field "gcurrentN