Great that you’re thinking ahead about the way to approach invoicing and credit terms in the future. This will usually take the form of
– credit terms – which you can vary by customer or channel. You will need to factor those changes into your cashflow
– legal requirements in the credit terms that will enable you to pursue debts via a third party if they go unpaid

Hopefully someone will reply who can share a suite of templates with you – easier than reinventing!