1. front gladhand leaking is either a bad 2-way check-valve under the drivers floor(top one) or the system charge check valve down in the bumper below the red gladhand. When you apply air to the red gladhand when towing the vehicle, it applies park air to release the towed vehicles park brakes, and it charges the air tanks so the blue service gladhand can remote control the towed brakes along with the towing vehicles brakes.
2. the stop light, lights along with the front air rear air idiot lights. with air tanks drained and engine off, these 3 lights plus low oil pressure and the low air warning horn in the dash should come on when the ign switch is turned on.
3. The drivetrains are pretty noisy, the hub gears add a lot of noise. you need to note the frequency of vibrations to try and determine what is making the vibration. at the overspeeds these trucks run at(DS angle vs RPM is above redline at highway speed), it is absolutely vital that the driveshafts are perfect(balance, slop, indexing). a thrown shaft usually wipes out the transmission/transfer.
4. What CTIS lights are on solid? All 5 on solid = internal BIT failure, and the module is toast... Sadly not an uncommon situation. you can try hitting it with a hammer

mine was like this when I got my truck, replaced it with 3 switches and a pressure gauge for manual control...
I have several utube vids on brake, electrical, plumbing, fuel sys and hydraulics. search for username "Rronmar"(3 R's) on Utube to find them...