I've jumped from Opererp 7 to Odoo 10 Enterprise.

In Openerp 7 a simple formula in Workflow...

Settings > Technical > Workflows > Workflows). Then, add the following condition in the two order_confirm transitions (between draft & sent to router nodes): partner_id.credit_limit > partner_id.credit + amount_total (replacing True).

then Openerp would not allow you to confirm the order unless there was sufficient credit. 

In Odoo10

As quote by Hieu Le 

Workflows in Sales, Purchases, and many other modules are going to be completely removed. Instead, we will use Python code

If I can stop the "Confirm Sale" button from being pressed because of lack of credit, then we can invoice 1st via..

Sales>Quotation>Action>Down payment (percentage)>100%

Unless anyone knows of another way or an existing module that would do this? Then I see two possible ways forward...

Option 1

Find the "action_confirm" (not found yet) and I assume extend the code to include a credit limit formula - this sounds simple

edit Option 1.5

I found an exiting module such as this "Partner Credit Limit" Sadly its for odoo 9 :(  Perhaps I could modify it.

Option 2

Write a short module to interact with the confirm process - would call upon my limited programming skills

Could anyone please shed further light on the way forward? (see below)