Your device is on DSA. This script should get you going and also get the switch config to show up in LuCI after a restart.
That answers #2 and #3. For #1, you'll need to check your /etc/board.d/02_network for pointers.
Thanks! And you are right, I was mixing the "old" Switch item in LuCI ... that's non-DSA. Appreciate the script, will give it a try.
I just need to dig into VLAN again - always confuses me . LuCI seems to allow me to set Egress (tagged or untagged), I need to find (remember) about how to set it for Ingress (i.e. accepted or not). Also how to make sure that the VLAN allows access to the "CPU", and what the heck Local means ... LOL.