I've also been thinking about where to attach the arms. Most of the replicas I've seen have the arms attached on the upper side, about halfway from front to rear. The Disney version is attached at the bottom. It would be nice to have the arms move along the track but that just doesn't seem worth it. I could, however; possibly design it such that I could detach the arms and move it around... something to think about.
I haven't checked the dimensions on my model yet but at first glance, it doesn't seem to off. I suppose I'll finish up the body first and then check the dimensions before moving onto the next section.
Another thing I've been thinking about are the speakers. Besides the obvious place of putting one on the charging panel, I would love to add additional speakers elsewhere to give him more oomph when speaking.
One last thing I want to mention is where to put access panels on WALL-E so I can install and work on him later on...