You can only select one plan per creator.
If a creator has multiple plans, the range of posts you are able to view depends on the price of the plan you've picked.When you support a more expensive plan, you will be able to browse all posts for plans that cost less than that plan.
Example:
Plan A 500 JPY (approx. 5 USD)…You can view all posts that are public for people with plan A.
Plan B 1000 JPY (approx. 10 USD)…You can view all posts that are public for people with plan A or B.
Plan C 5000 JPY (appox. 50 USD)…You can view all posts that are public for people with plan A, B, or C.