Can too hot water cause the mate gourd to break?
I don't think it's your fault. Mates don't break that often. Besides, I've seen a lot of people drink it hotter than me without any problems.

As for preparation, it was recommended to me the following:


Place the leaves in the mate  
Add a little bit of cold water  
Add hot water


When and how you put the straw is a whole other chapter!