Q11_

I’m thinking you maybe also could ad an option where admins/moderators could accept or deny them for whitelistning.

The way it could whitelist people on the server is that the wp plugin works in a MySQL database. It would also require you to make a minecraft plugin which could read from the same MySQL database, to see if it can let a person in or not.
It should be able to use external MySQL databases. And the great thing with this is, that you can have multiple Minecraft servers using the same whitelist 😀