it is hard to say what are the requirements for the Panorama in Azure, it is also important to know what are the use case.
When you logs/sec are lower the 10,000 and you didnt want to manage more then 500 Devices then are the min requirements:
Then you can use a DS5_v2 vm instance type
1. there is no version requirements for Panorama in Azure it is again depends what are you trying to archive here but i use in the past the Version 9.1.4
2. I have already a lab running in Azure Panorama HA and i can't complain. It works really stable for me.
I hope i could help.