Customer credit approvals - workflow

E1  8.10

I'm looking at activating workflow messages for our credit approval process, and would like some guidance on how this works.
I have a few queries after reading documentation:

1.  Does this has to be setup globally or can it be done by company?

2.  Is 'credit limit' the only field that invokes the approval process?

3.  How can the actual approval message be approved, what is the application to do this?

Any assistance would be much appreciated.

Many Thanks,
Andrew