Wow, a little tight but as they say an inch is as good as a mile! I'm glad it worked out for you as planned. Your set up looks really nice!
I was a bit surprised to hear that it towed in fifth; my truck will tow in 6th gear with no problem, but it also has 3.73 gears, smaller tires being a dually, and I'm sure a different ratio in the transmission being it's a G56 manual. You will be very happy to see how it tows in the mountains; we went over Stevens Pass about 6 weeks ago and I was in 5th gear for most of it and down to 4th for only a short time. I only had one brake application going down each side of it too.
I agree that the DEF is a non issue. I have topped mine up half a dozen times since I bought the truck and 1 jug from Wally World always brings it back up to full. I usually wait until it is at about half or less and it will then take the whole jug.
Enjoy!