Newbie question about Vault 2i

I am about to order my new home theater and I am planning on buying Vault2.  I have Ethernet set up in closet where the gear is. 
I am planning on converting my CD’s and also signing on to either Tidal or Qobuz.  
The way I understand it is whatever music I download will be stored on Vault until I drop service.
Vault will be connected to my new receiver.
I will access the music via my iPhone and iPad, correct?
will a subscription to Roon make it easier to use Vault or is the software easy enough to use. What is the Value of using Roon?
Would converting to FLAC be the best option. 
Is connecting to receiver via rca cables to analog out the best way to go
if I didn’t care about converting CD’s would Node 2i be a good option for a lot less money? Is there an advantage to storing Tidal files and Qobuz on on Vault rather than just streaming Tidal to Node 2i.
thanks 
Bob