You can still install the plugins either individually from the play store or you can purchase a bundle from memory using the AutoApps app from the play store
To answer your question, the plugins are not required as such, only if you want to use those features. Sometimes there are alternatives, but particularly for notifications and alike they are required. For things like AutoRemote and Join I would strongly encourage looking at the http server options available natively in the app now, including in 6.3.