Is it possible to configure Online Store redirect that will take a customer to a specific Service Plan with some additional resources already added to the shopping cart? Or redirect customer directly to checkout screen?
There is no such functionality in the current version of PBA, it is going to be added in the future updates to the product in scope of the request PBA-33575.
As a possible workaround you can create a separate service plan with already included resources. Then, create an Online Store redirect like