@Steve10, I think you could at least avoid the extra seat consumption by using non-company-domain auxiliary email addresses (e. g., gmail.com).
And you could benefit from a Gmail feature such that you’d only need to create a single new Gmail account:
Create a single Gmail account like stevecoaux@gmail.com. For each different third-party, just start using addresses like these (a “+” followed by the role/name):
stevecoaux+legal@gmail.com
stevecoaux+accounting@gmail.com
stevecoaux+website-developer@gmail.com
Hope that helps.