For a top door, the Alexander, Barney or Borneo may be best then
The Borneo really needs a full level in my opinion - or shelving similar to the Alexander with something blocking the hole in the middle/over it.
Sisal string or rope is safe for hanging things from the bars - not sure what the clips are like but they can get feet/legs or even head caught in clips.
Ears flat sounds like he is feeling a bit nervous of the open space
It can be for different reasons. Ears are often down when they haven't fully woken up, or if they're not happy, or just feeling a bit exposed, but if he seems fine generally I shouldn't worry.