Single port Meraki MR18 as router?

I have a Virgin Media SuperHub 3 cable modem/router and a Meraki MR18 running the just released LEDE 17.01 (awesome job BTW, instant improvement in wireless performance vs OpenWRT!). The MR18 is a device that has one ethernet port and 3 wireless radios. Both hang off a generic NewLink gigabit switch and I have quite a few wired and wireless devices dotted around the house.

As anyone who has ever owned a SuperHub will know, they are useless, like so useless they don't do internal DNS and there is no way to change the IP from the default 192.168.0.1. I've managed to reduce the crashing by disabling the wireless and DHCP, but it still has to do firewall duty. Everyone on the forums says to use it in modem mode, which I'm not entirely sure how that works, but I think it's a cable<->ethernet bridge and the router needs to get DHCP off it.

Is there any way at all to get my single port Meraki to do the routing job, even if it requires all my wired devices to have a VLAN set, or is a 2+ port router essential for this job. I don't mind if it's ugly and hacky. I don't even mind having to unplug my other devices when it's time to reboot either the Vermin hub or the Meraki. I know that sharing the same bit of wire in 2 directions will be unfun, but a 50MBps cable connection seems unlikely to cause a problem when my home network is gigabit.

It's a medium-term solution. I also have a SamKnows SK-WB8, but I'm suppossed to be participating in their monitoring scheme until October, so don't really want to be hacking that until I've fulfilled my obligations there, given it's a device I got for free, and all.