There are a number of parameters the car needs to meet in order for stop/start to work. The parameters are listed in the owners manual. Some of the parameters are battery power needs to be above a preset level, coolant temp is above a preset level or the outside temp and ambient temp difference is not greater than 5C etc.
I know nothing about tow bars. If you are on Facebook joining one of the GS group will give you information on towing as a few members on there have experience. Witter tow bar is a name that came up all the times.
No I didn’t remove any wheels at all. The rear ones are abit fiddly as you have guessed the lack of space. I have a little horizontal ratchet screwdriver which is only 10-15mm tall plus the length of the self tapping screw is small enough to fit the space behind wheels. Taking the rear wheel off will be much easier to screw in though. I too have a some metal clips. Without instructions I just clipped it where I thought it was a good place. Taking photos is not a problem but posting on here might be. I will give it a go later if I can.