Thank you for pointing out the mobility considerations, I didn’t think this through properly.
I managed to create a hybrid config with wifi1 and 2 on CAPsMAN, while wifi3 is configured manually for backhaul, but the it’s not working too well.
I created a separate thread in the Wireless Networking section for this - http://forum.mikrotik.com/t/audience-backhaul-issues/180839/1