Is this is more of an inquiry /quotation than an actual sales order?
If the customer should provide the exact details at a later time and you are not expected to do anything with his request until you get all the data, then probably you can create the order when you have all the information that you need?
The approvals, which have to be collected, are not related to credit management checks - is my understanding correct?
If you need to ensure that the customer would pay before you initiate any further activities, such as providing design etc., then you will need an order anyway - at least to cover the work on the design, but it could be just for the initial service and you don't need requested delivery date for debit memos.
These production/artwork approvals - who and how approves that? Is this some project-related scenario, where the customer has to approve the design before determining the exact product properties and initiating production, but you cannot estimate the exact dates?
If you decide perform custom modification of the standard logic related to KETDAT to make it optional for standard sales order processing, you risk to cause inconsistencies.
It would be safer to create the order with some requested delivery date (based on rough estimation or based on some pre-agreed timeline) and with delivery block, which resets the confirmed quantities (because you don't want to reserve any stock, when you don't know if or when you will need it) and after you get confirmation that work can be started, to remove the block, set the correct dates and perform scheduling.
If you collect the approvals in SAP and not by receiving some e-mail from the customer, you can probably use status profiles to record them, so until you collect all approvals the order can remain with zero confirmed quantity.