I hope this is still interesting for others reading this thread - perhaps we should move it off on to private messaging? (or simply emails?) - In any case one factor that comes to mind. If you are not intending to have rotatable antennas at the farm site. You could keep the transmit station where you are and only locate a cheap receiver out at the remote site. Then you don;t have to worry so much about an ATU.
Just a thought.
That AT857 - is that the LDG one or do Yaesu do one? In any case as you say if it’s controllable via the CAT port, it should also be controllable remotely.
What will you have in the shack? do you kep the head of the 857 in the shack and the body goes remote, with a hardware remoterig box at each end, effectively extending the RJ45 cable?.
You may wanty to look up the other thread on this reflector as a Spanish SOTA chaser has just done the same as you are planning - let me see if I can find the thread and then update this post, so you can read what he did.
73 Ed.
Here you go: