On a Pro plan (or any plan!) you can make as many bases as you’d like, and it doesn’t affect how much you pay to use the product. The number of bases you can make is completely independent of the cost of your plan, and as long as none of the bases you make exceed the per-base record limits described on the pricing page, your bases won’t have an effect on your plan cost at all.
For self-service premium plans (Plus and Pro) workspaces are upgraded, not accounts. When a workspace is upgraded, all bases within the workspace will have premium features (other workspaces will not be affected). Billing is based on the number of people who can edit (or comment on) at least one base in the upgraded workspace. Read-only collaborators or people submitting forms are free.
