I'm going to answer what I can: Q1) This completely depends on your environment. I can tell you a VMX doing nothing (i.e. freshly deployed before any traffic is sent to it) is de minimis, but in a live environment, this is entirely related to what you have in azure, if you are using the vMX just for site to site traffic or if you are using it as full firewall as well. Q2) You can upgrade your license from S to M to L, XL has been discontinued. You would have to redeploy the VMX to do this, but the config would be saved in the dashboard. Its functionally equivalent to swapping MX models in a network. Q3) I've never had to tune anything and the documents you link are referring to 3rd party vpn setups not native Meraki SD-WAN. My environments are pretty simple so others may have some thoughts. Q4) I'm not aware of any Cisco Safe guide for Meraki. Q5) As far as multiple Azure Subscriptions I would always use vnet peering inside Azure to link Subs. It's going to be cheaper than using an appliance. Now you could have more complex security requirements and at that point you need to identify your needs vis-a-vis the available solutions. Regarding logging, you have the same logs you do for any meraki in the dashboard. I've never needed to refer to any azure logging beyond deployment errors and those were usually fat fingers, but others may be aware of something else. Given the depth and breadth of your questions, I do strongly suggest working with your Meraki SE/Partner and discussing details of your actual environment. It sounds like you could have quite a complex setup and we can mostly answer in generalities.
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