normally i would say …OT first…then A4 and the MD…
but since i have noticed that the MD is slightly late in midi clock, maybe it would be better to connect it as master…run a simple test with a click on each machine and compare if there`s any lag of the MD. then decided whats best for you. lucky me i have an acme 4 so i can pull the MD a little forward a few ms. dunno if it works when putting the MD as master…but’s worth a try. 
also u can use the midi ctrl machine to mangle the OT then 