In Pro Sites, you can set the minimum level where that plugin is available. So if you enable a plugin for the Bronze level, then Silver and Gold will have that plugin as well. If you enable it for Silver, then Bronze and Free would not have it.
Is there a way to support a la carte premium plugins? So for instance you have a base package with a bundle of premium plugins. If a user wants to purchase acces to a "add-on" is there a way to support this?