Can ARC download "all" new music automatically?

I recently upgraded to a 1TB iPhone. One of the reasons I went with so much storage is to be able to have all of my Roon music (~1,600 albums) downloaded and available locally on the device. I’m hopeful this will make Roon ARC playback more stable when the cell signal is spotty. I’ve kicked off an initial download of all albums and starting to consider how to keep my Roon ARC downloads up-to-date. Rather than periodically downloading new albums as I add them to Roon, is there a setting or method to have new albums downloaded automatically? Perhaps Smart Downloads is an option? I want to make sure that Smart Downloads doesn’t delete anything unless I’m running out of space and its behavior isn’t clear to me.

Obviously it’s an Apples to Oranges comparison but Apple Music on iPhone has a setting to download songs automatically as they are added to the library.

Also, am I correct to assume that if I’ve downloaded songs they will be played back from the local storage rather than being streamed from my Roon server?

That is correct.
And about your first question, I think smart playlists are indeed the way to go.

I do this with a smart playlist (called everything) generally works pretty well.

Thanks, @Arlen @GregD. How do you create a smart playlist that includes all tracks in your library? I tried creating one but couldn’t find a combination of filter options that included everything across my 2x storage locations.

Mine is based on storage location. I only have two - ROCK internal storage and Qobuz.

You can’t download Qobuz tracks anyway - so I just use internal storage.

Like @GregD said. Don’t forget to change the sort order to ‘album title’, if you don’t want the playlist in a random order.