Local mesh - volume 100 GB.
Well, if you use such terminology, you would be better to invite an outside specialist.
Network with branch offices through VPN. The ATSK out one interface out - phones branches may knock directly, then the connection will not fall off in case of forking the VPN.
On the server under the telephony to put Asterix, and on the same server to deploy Mikrotik for routing.
Yeah, and when a server falls, it will fall and the entire network. Don't ever do that, buy separate Microt.
Two servers - one for 1s and the other in telephony.
And a file? AND AD?
You can not confuse the office wires, and buy a WiFi router and WiFi-whistles in every computer.