How long before I can drive on it?
Usually around seven days for foot traffic and closer to a month before a vehicle, though your concreter will give you the number for the mix and the weather. Driving on it early is the most common way a good driveway is ruined.
Why do quotes differ so much?
Almost always preparation and reinforcing rather than the concrete. Ask what depth, what mesh or reinforcing, and what base is going underneath, because those are what decide whether it cracks in five years.
Do I need a vehicle crossing permit?
If the work touches the footpath or kerb, yes, and it comes from the council. Many concreters handle it, so ask whether it is included or something you arrange.
Can concrete be poured in winter?
Yes, but it cures more slowly and very cold or wet conditions can affect the finish. A concreter working through winter will plan around the forecast rather than pour regardless.