Woah - I'm amazed by the amount of replies! Thank you all!
Replying to the more specific questions:
What thickness of XPS are you using?
I generally cut my XPS with my proxxon cutter. Honestly, it's a VERY CRAPPY tool, highly inaccurate and all, but does the job for this kind of buildings.
This considered, I generally try to cut a 5 cm thick XPS into four sheets, so they range between 1 and 1.5 cm each.
May I ask when you were able to visit? I was last there in 2011
I went to Ganzi/Garze in 2019 right before the lockdown - it was a fairly intense trip, mostly hitchhiking and local busses, and i made it to a local artisan who made pottery out of black clay. I spent there 3 nights and did my own tiny pottery thing while living with his family!
...Speaking of which, starting from a picture found online we selected two first vases:

...and we sculpted our own!

Updates soon-ish, real life permitting.

Jack