I finally got started. Today all I’m doing is hanging the indoor units.
To avoid cutting the molding, and make this an easily reversible install, I used 3/4” plywood to space the mounting point out from the wall and catch studs.
My wife inspected the initial hung unit and her water has not broken, so I’m ok. She is surprisingly uncaring about mechanical and systems stuff, the baby cows emerge over a vase thoughtlessly repositioned or an improperly fluffed pillow.
So of the two, I’m the one more bugged by the gap between unit and wall. Later on, I’ll find some easy way to fill or cover up that void.