Here is a link to the Feldon calculator:
It should help with all your measurements.
#2 Whatever you want. I put mine on top and extended it down to just above the top grate. The top hinge for my door is almost top-dead-center so my exhaust is offset slightly to the back. Works with no problem.
Oops, see you already used a calculator. PS, if the calculator says you need a 30" pipe, I've always taken that to mean from the top of the cook chamber. So if you extend it into the cook chamber like I did or have it mount on the end of the tank, you will need to add to the length from the calculator.
Best of luck!