MPG? again, string.... a good 'supermini' should be well into the 40's for a petrol, and nearer 60 for diesel, a larger car will use more, but will depend on your driving style, town or open road, many factors to consider.

Tyres are normally 'all year' types, stick with well known brands and you won't go far wrong, would say a separate 'winter' set unnecessary in the UK, unless you're planning to move to the wilds of Scotland or Wales. ditto chains.

Extra kit? Would add a wind up torch to your list.