Would MacBook Air 2018 handle a constant run of a Windows VM for the Development
In general, MacBook Air's can handle run anything constantly, that they can handle running for a short while. You cannot "overwork" the computer so to say - it won't suddenly break or stop working for that reason.

And yes, MacBook Air's in general can handle running VMware Fusion (if the model you have is supported by VMware Fusion). You decide yourself how much RAM you dedicate to the virtual machine, when setting it up - so 16 GB will make it possible to run multiple virtual machines.

If you want to have a clearer idea of the amount of RAM needed, you'll need to setup the system you want and check how much RAM it uses.