Nice write up! Couple things I thought of:
1) Is there a fire extinguisher bracket inside your loader? That might be a good mod if there isn't, and keep an exstinguisher with you (that leads to my next point)
2) I would be VERY concerned about installing a cheap plastic fuel filter, maybe I'm just overly cautious. Please don't take this as disrespect, but IMO, I think it could be a 'weak link' in your system and a potential 'future' fire. Diesel's vibrate, skids get knocked around, and should the filter crack and leak due to age or poor mfgr, which I think is a very real possibility, all your hard work would go up in smoke before you could do anything about it. With the cab and all, you wouldn't even know if there was a fire back there until the unit quit working and by the time you saw it and got out of the cab, it would be too late, probably even with a fire extinguisher. I don't even know if a regular homeowner's insurance policy would cover a burnt skid loader, unless it is specifically added?? Anyway, that would be a shame given all the work you've put into it. Maybe it's just me but I've seen more than a couple fairly new NH skids that were burned up for sale on the internet (for parts), maybe that plastic filter was the cause?? I even looked at a burnt NH in person as a possible rebuild, priced up the parts, etc. The one I looked at didn't look too badly burnt, but given the cost of parts, and the amount of electronics, major re wring, and all the half-melted aluminum engine parts, even if I did all the work myself, it was plain to see a small fire renders a modern skid cost prohibitive to repair. I would consider hard-piping a separate remote diesel-rated canister filter in an easy to get to location away from the top of the engine, and ensure all your new electrical work is secure and well protected. Hard-piping projects are fun too, to get all the lines bent and looking nice. After seeing that burnt skid loader I looked at, I keep a fire extinguisher in mine all the time.
3) Rear Door Hinge Mod - I don't recall what the rear door hinges look like on your NH model, but for most skid loaders, the rear door hinges seem to be poorly engineered and due to the weight of the door, they wear funny and sag after time and look like crap. Is that a possible future problem with the NH 220?
Other than that, great work. I like the Mirrors idea. Something I'm going to replicate on mine. I don't work around trees too much.