Media Server & Player (Smart Home) for 20 Zones

Hello together,

first of all I hope you are all doing well besides the current situation.

At the moment I plan to build my own house with smart home and this should include also a multiroom audio setup.

Here are some of the current facts:
- 20 Rooms (Zones)
-- 18 Stereo
-- 1x 7.1
-- 1x 5.1

- Input Sources
-- Spotify
-- AirPlay
-- Beamer (FireTV, AppleTV, PS4, Xbox)
-- Smart Home applications (door bell, announcements, etc.)


My idea is to build a 19" rack server with multiple (4-5) on-board (PCI) soundcards. (The server will also be used for iobroker and nfs storage server)
This server then should hold the LMS as well as all the squeezelite (or other) players to enable the multiroom setup. (The output of the soundcards then goes to an amplifier also in the 19" rack)

My questions at the moment are:
1) Is this a good idea? :D (I stole it a bit from the Loxone Media Server (but I think 3k are too much for the media server itself))
2) Do you now any good soundcards which I could use here?
3) How do I integrate the audio soruce from my Beamer (7.1 Sound) (HDMI ARC or optical cable)
4) How do I integrate the audio from my home automation (announcements, door bell, etc?)


Thanks a lot!

Best,
Tixa