As long as it has connected to the Dashboard via WAN 1 at least once before: yes (in case NAT is not an issue regarding Azure VPN looking at your other question, but I‘m unable to answer that one).
Yes I have done this a few time before and it works well, but as previous poster confirmed you need to connect on WAN first then once 4G is established you pull the cable and every subsequent reboot will fail-over to 4G no problem. As for Azure, that I can't confirm.
As soon as your MX is connected to Meraki cloud and has reachability to the peer it should be working but building an IPsec tunnel on cellular is never considered as a best practice, the best approach should be using the Wan interface.
To make this work you would need to get your cellular provider to give you a static IP address with no inbound filtering.
Very few carriers do this globally. So you are not likely to succeed using this approach.
Your best bet is to deploy a VMX into Azure and use that for the VPN. It will work with 4G connected MXs.