Hello Ryan_1994,
did you check the standard "Sales Invoice Credit Limit Approval Workflow"?
I guess this could be your starting point.

You can use this one that checks if the Customer Credit Limit is exceeded taking into account the Invoice amount sent for approval.
Also, you can create a Workflow User Group for the Finance (and other) departments and send the approval request to them.
I hope this helps you to move forward.
Kind regards,
Vanessa.