Re: Migrate Catalyst to MS120 but the Firewall its ASA5508
To add to @ww 's comment, you only need the management port for initial configuration. Once the switch is up and running and connected to the Internet you don't need to use it anymore. In fact if you can plug in the switch to somewhere where it can get a DHCP address you wont need to use it at all. It just needs to connect to the Internet once to be able to download its config.
You can get the MS120 to use vlan 228 for its access to the cloud via the local status page and configuring the "uplink configuration":