I wrote this up a while back in related post from you 
See http://forum.mikrotik.com/t/a-very-simple-redirect-to-an-http-page-after-join-wifi/165960/1
You can follow the Pi-Hole example, to enable containers - just use a different mount and envs & /container/add would use “remote-image=nodered/node-red”, instead of =pihole/pihole when creating the nodered container.
The NodeRED config is in above link.