Wow!! You are really banging this out. Very impressive. Just as a suggestion, I would suggest tying the two perpendicular Panels together with either a sheet or bat, as the top round corners, hanging out like that are going to resonate. It looks very professional, and extremely well finished off.! This is a great thread, one of the best.
On the top back there is a simple spool holder that looks like this. I have been thinking of doing a threaded rod across and turning the spool 90 degrees. On the mendel90 they often use a teflon tube (the white tube in the right top corner) to guide the filament to extruder, my extruder does not have the tube. So I feel the spool needs to be turned. Still working this out as I get the wiring done.
Turning the spool, especially with a variable speed feed, will relieve pressure on the printing head. This is where I see these things mess up the most.
Very interesting idea to build your own 3d printer. I thought about it.... but only thought about it.I like turn key. But I am following this with great interest.