One quick thing to point out about the rear 3pt connection - in my set-up I did NOT replace the M18 to NPT adapter there like I did on the side of the loader valve. I didn't have a need to since it was in & working.
Just wanted to make sure you knew & suggest you use the M18 to 1/2" JIC there. (I would also suggest NPT to JIC on the subplate as well) JIC gives you the ability to spin/swivel the hose during install and is much cheaper than an NPT swivel fitting.
Depending on where you end up mounting the valve you might also think about using 45 or 90 deg JIC fittings on the hoses to help with routing as they can make a sharper turn than you'll ever get out of the hose itself w/o kinking it.
As to the filter question, ours got mounted to a flat plate and pointed downward in roughly the same location (maybe even a bit lower) - from how I picture yours in my mind I like yours better as it looks like it would offer much more protection from limbs, rocks, etc underneath the tractor.
Good luck and keep plugging - you'll get it worked out. :thumbsup: