My Run Room is 23' x 69' with an L shaped area for running. My website gives a lot of information that applies to large DCS layouts.
You will probably be happiest with your TIUs centrally located. See my track with the Self Guided Photo Tour.
My 4 TIUs are centrally located under tables on control carts. With really good batteries in the remotes I almost always have train control. When the trains don't see the remote they continue running per last instructions. Once trains are entered into your system they don't care which TIU they see. You may not need yours on the ceiling.
My AIUS are centrally located near the control panels, because I used the terminal strips in them for wires from turnouts to control panel.
Your AIU placement plans should work very well. It's worth a try. Here's a previous discussion on boosting the AIU power if needed.
