Hi Tom,
I get my AdBlue from Amazon - £14 and free delivery last shout. 20 L lasts around 10,000 miles and 20l will fit in the tank when the warning is live. I would not chance brimming it - it's not hard to top up and note its corrosive so you don't want to be splashing it on all over....
I have not found the S/S that intrusive and with Hill Hold on as well you can sit stopped with no feet on the pedals and then just depress the gas to pull away. During the winter it will S/S less anyway. Is turning it off that hard to do (One other option is to keep it in Sport mode on the drive select)
I am using Virgin Mobile SIM - Networks are all much of a muchness. I pay £9 / Month for 2GB (double up for free) and they roll over what I (the kids) don't use to the following month. In car internet is a nice to have and the kids browse via their Tablets on long journeys. Google Maps and the search is great but now the honeymoon is over it is rare that I use it that often.