Permanent connection between 20 buildings and a central server in remote location

Hello,

We have 20 buildings where we have a local HVAC installation. This installation needs to be reachable via a central server in another location. Every building has an internet modem installed which I don't know the details from. I don't know what subscription is attached to it etc and assume it has a dynamic IP.

My idea was to make a Site2Site VPN connection from every building to the remote server so the server can reach each installation locally. At the moment, there is no firewall or router in place in every building so I need to come up with a solution.

My idea was to buy an Ubiquiti EdgeRouter Lite X in every building and set-up S2S connection to the remote location. Are there any better solutions available? What should I pay attention to? Can I have a problem with the dynamic IP assigned?