connect + NAS + chromecast W/OUT desktop

[bookjason]

hi all! i'm a n00b to spotify, but having trouble finding out if i can set up my house the way i'm hoping. my plan is:

:: a few sets of powered speakers, each with a chromecast audio connected

:: an apple time capsule (network drive) with a folder of mp3's living on it

:: an iphone as a remote with google home app and spotify app installed

:: a google home 

in theory, it apears that i can open the spotify app on my iphone, select some music from spotify, and cast/connect it to multiple chromecast-enabled speakers simultaneously, giving me the multi-room audio i want. is that part right? (and as a bonus, i can talk to the google home and tell it to play spotify on all/any speakers through the house.)

will i also be able to tell spotify that i have "local music" stored NOT on a desktop computer, but rather sitting on the network on the time capsule? or can spotify not recognize those files if there's no spotify app installed and running directly on the time capsule (which doesn't run apps).

any knowledge of whether the above will work would be great... or if not, any suggestions of how to achieve the above! thanks in advance.   =j