You can access the left front by using a large hole saw in the forward most cabinet, use a hole saw large enough to get your hand in there. No cabinet will have to come apart by doing this. I had to do this to tighten the hold down that came loose.
Your truck should have a tire info sticker on the driver's door jam area, this sticker will tell you the tire size the truck was equipped with from the factory.
Leaking? Plugged up? No need to change, stainless lines offer protection for competition because of high heat in the fluid from braking. The vehicle being only seven years old and only 100k, the lines should be just fine. It would not hurt to flush the system out and change the fluid if very...
My '08 Hawk when installed onto my 2015 Super Duty was the same, low in the rear. I added a strip of wood on the rear edge of the camper bottom to level in the bed.