No, it’s not necessary to set supplier rules for all of your clients’ suppliers.
Suppliers who are only used very irregularly, or on a one off basis, are not suitable for supplier rules. There’s no point taking time to create supplier rules for suppliers who aren’t used very often, and are used in a different way each time.
If there is a supplier where some of the information changes, it is possible to set a supplier rule to cover only some data points.
For example, Amazon purchases might be similar in terms of payment status, tax, etc. But very different in terms of category or project associated with the purchase.
In such cases, you can set up a supplier rule with some information missing, and input it later.