Meraki Go APs use the same meshing technology as our normal Cisco Meraki APs so they will be able to form a mesh connection with other APs in the same Meraki Go account wired or wireless. You can see their status (wireless/wired) on the app in hardware menu.
To my knowledge you can have up to 20 Go APs on a single Go account.
Chiming in to confirm that Roska is correct;
There is a limit of 20 Meraki Go APs per account and the APs that will be meshing do not have to be wired; however the root AP is typically wired in this scenario.