Hi @csteele & @steve.maddigan, thanks so much for your answers 
Okay, I understand that I need to install a Hubitat device in each building. So, the only kind of "extender" for Hubitat is another Hubitat itself?
What about this thread, for example? Harmony Home Hub Extender – doesn't it also extend the Hubitat network?
And regarding what I wrote earlier, "I'm trying to figure out the best strategy to extend the network without having to modify all devices if I add a mesh or repeater for the Hubitat (I read about this in a forum thread but didn't fully understand it)," does that ring a bell? Will adding a Hubitat in each building also solve this problem?
Thanks so much for your kind help!!
All the best,
Yiannis
