Thanks for the reply, yes we cannot add ethernet due to cost and understand the consequences with mesh and throughput and connectivity not dedicated versus an ap on LAN. Management wont approve additional cables.
All mesh nodes will use the same channel as the gateway they're connected to. That means that worst-case your entire network will run on 2 channels... or you might get lucky and be able to mix some on 2.4 and some on 5Ghz... Neither is going to be a great experience unless you have very few devices and/or vary low bandwidth demands. This is going to create a massive "hidden transmitter" problem domain.
I second the push for as many cabled nodes as you can manage. 2 is better than 1, but 4 or so is probably a bare minimum for the 12 APs you want to deploy. You really want to make sure that each repeater can talk directly to a gateway.
I tried to contact Meraki when a distribution center was first sent and inquired as to whether they could sign on and examine over the occasions and simply affirm they are seeing no issues before it went into generation - all I got was 'on the off chance that you don't have an issue, we don't have anything to check' was not so much the appropriate response I needed...