Can members of the same workspace be on different payment plans?
Within one workspace, there can be only one kind of a paid subscription, the subscriptions planned cannot be mixed. Regardless of the subscription plans, users can still add free members.
Can I pay for my subscription separately from other workspace members?
If you want to use a different payment method, you would need to create a separate workspace. There can only be one card per workspace, so if you're an admin, and want to upgrade other members' subscription, it will all be charged to one card.