You might as well get one, it works well with the Avant.
You can use your BeoOne Remote very easily with it.
Although I have had no issues with an Apple TV, no device is fault free.
Where is your DVD Player being installed? Is this solely a DVD or a BluRay? If so I would have a BluRay installed as that still plays your DVDs - if you wish to opt for Physical Media.
Have you the Motorised floor or table stand?
I ordered a clamp from STB Brackets and installed on the clamper system my PS4, Foxtel (SKY for you), and my Apple TV.
Although there is a space in the Avant that can house the Apple TV, with the back panel on, in my opinion there is not enough air flow and this in time could cause the Apple TV to fail and it would be hard to get at if you have to reset it or whatever - that's why I had it installed on the outside. At least with the motorised floor stand this would be a bit easier to get at - but with the table stand, i feel it would be difficult.
One dealer said to me that if i had the Apple TV installed inside the television then they recommend that the back panel of the TV is not installed on that side because of air flow which makes sense but isn't as great aesthetically - although you rarely see it.
Can't wait to see the pictures of your install. Good luck.
I haven't signed up for Spotify and I was using deezer the other day on my PC and thought it was excellent. So if i were to sign up to a streaming service it would be deezer. And being that the BeoSound moment has Deezer access - if i purchased that in time i would just want one service, not two.
You would use Spotify or Deezer natively through your Avant and not via the Apple TV.
Good luck