First time OpenWrt / LuCI user, help setting up firewall and vlans

Hi Folks,
I'm new to openwrt but not to linux and networks, I'm attempting to use luci to configure a mikrotik RBM11G running OpenWrt 22.03.0 r19685-512e76967f / LuCI openwrt-22.03 branch git-22.245.77528-487e58a

Here's what I'm trying to achieve:

The openwrt board is acting as AP and IP gateway to pass traffic on to a network bonding and acceleration device. This device has an ethernet port with three gateway interfaces on three VLANS that are used to separate different types of traffic for different priorities and bandwidth limits etc.

These gateway interfaces are on a stub /30 network so only two IP addresses are available for each VLAN this cannot be easily changed and thus leads to the need to NAT traffic leaving the opernwrt.

I want to have an SSID for each VLAN as well as the ability to use the openwrt as a gateway to the bonding device for tagged traffic on the LAN, with the openwrt allowing routing (or just network overlap so they can all be on the same subnet) between wireless and wired devices. DHCP should be available on each VLAN too.

So I have two tasks:
1) Get SSID traffic tagged with a specific VLAN.
2) Perform NAT on outbound traffic for each VLAN and send it on to the appropriate gateway

To simplify things I'm only dealing with one VLAN right now, VLAN 70 with a subnet on the WAN side for communicating between the openwrt and the gateway device.

I'm open to suggestions or complete recipes here!

For a start I am confused by the two possible places where NAT masquerade is configurable. There are masquerade tick boxes in the luci interface on the firewall zones list, but there is a whole tab for NAT rules too, does the zone list tick box act as a general override to any NAT rules?

Can anyone help with any of the above?

Many thanks,