First off Welcome!
I will try to answer all your questions short and sweet, and I'm sure some will add further.
1: Engine and trans are reliable. I would def get a 4.0 if possible. The five speed is good, the six speeds mine as well be five speeds unless highway driving. Durable, I think they are. However, that all depends on how your treat any vehicle. Good thing parts are fairly inexpensive.
2: Being 6'1 will not be crowded for you, you will not be able to have anyone in your back seat behind you though, seat will basically be all the way back.
3:No get up and go, all torque, getting a running start and try to plan your passes of cars ahead of time...funny but that how I do it.
4:MPG I think it is fair to say most of here get 14-18 nothing more, can always be less, TJ's are pigs.
5:Leave the engine alone
6:Towing is VERY limited. Max is 2,000lb and with the SWB (short wheel base) I wouldn't tow a 12" pop up but towing opinions is one of the most argued topics on this website, so form your own opinion from others...I would not.
7:Very easy to work on, easy to do wires, no you can't rebuild the motor without removing, but yes, if you know you way are repairing vehicles it will not be difficult.
Good Luck, Hope you get one! They are a ton of fun!