Sorry for the slow response, i've been away in Dublin for the long weekend over there to run the marathon - don't ask how it went!!
To answer your questions:-
We're approx 10 miles from Basingstoke (just over a mile from Mortimer train station)
Parking is all onsite. So new is this run that we're not anticipating massive numbers first time around, but should it be required, further parking will be a few minute walk away.
The question of shoes is a tricky one. Even at that time of year, you'd be ok for most of the route in road shoes, but you might find a few short sections a little slippy. Two thirds of each route is off road though, and this includes a mixture of pretty firm gravel tracks but also fields that might be muddy come new year.
You will certainly get a cuppa afterwards!!
Andy