I would use a common VLAN for Meraki management. Personally I would use VLAN1 - but I like my life to be easy, and because the Meraki management interface isn't used to configure the device (apart from conncetivity to the cloud via the loicla status page) like it is with Cisco Enterprise kit - so the risk is much lower.
However VLAN300 will do just as well.
If you plumb all of these thorugh to your firewall at Layer 2, so they can get out straight to the Internet then your life will be easy.