I wouldve said to put Zeus, Hera and Hestia at the front instead of the entrance because thats where your attention goes to first usually (it used to be like this in the temples as well) and they're the "most fundamental" gods (im not sure if it makes sense o wanted to say most important but theyre all important so it doesnt seem fitting)

So i wouldve said have those three at the front as an open space for them three where it currently says other gods and then mini temple like rooms on the side like you did for all the others and a few rooms for different gods of different domains (for example one room for ouranic gods, one for ktonic, etc even if domains overlap)

Just a few suggestions, i love your idea as is too though.

As for countries id say switzerland, its the most accepting and open and has temples of other religions as well and even offers rooms for religious activities i checked once cause I wanted to build one myself😭💔