On the AP, (for a locally bridged WLAN setup) to create a 'trunk' port, you will need to at least add the VLAN entries in the Virtual Interfaces listing (no addressing is needed though for that VLAN unless using a service/feature that actually requires that the VLAN have an IP address)...and then in the ge1 setup, configure it as Trunk, set the Native VLAN, and then specify any VLANs in the Allowed VLANs list.
Understand though that with your current Tunneled WLAN setup - The VLAN traffic at the far end of the mesh is being encapsulated within the Mesh protocol as it traverses the Mesh connection. Once it reaches an AP on the other end of the mesh (with a wired network connection) it's decapsulated but then that VLAN traffic is still encapsulated within MINT itself. That VLAN traffic is then carried back to the controller inside of MiNT....which means that no VLANs have to be defined on the AP/switches in order for that encapsulated traffic to get back to the controller - If a successful MiNT connection already exist between the controller and AP, then you would be good to go. That's all it takes. You'll also need to define the VLANs (and setup trunk port) on the controller though because once those encapsulated VLANs within MiNT are unpacked inside the controller, they need to get off of the controller and back onto the LAN...so the controller's interface needs to be setup to allow for that.
Once you go with a locally bridged WLAN setup though, you have to take into account having trunk ports setup everywhere (APs and switches. Not the controller unless for some reason you wanted to also bring that traffic back to the controller).
To set the MiNT MTU in the CLI: (Set this on the controller)
#
config
#
mint-policy global-default
#
mtu
#
commit write
In the GUI:
Configuration -> Devices -> MiNT Policy -> (mtu=)
As for the MTU value, it's hard for me to say. But if you think that the network path won't ever change (between the APs and the controller) then you could just leave it at 1472. My suggestion to maybe lower it was just to act as a small buffer in case what appears to be the current 1472 MTU setting ever changed (lower).