It's about 60-70km depending on the route you choose.

You can take the toll A4 for part of the way, or you can just go through the country side (single lane road) like the bus does. Havent been on that road for a couple years now, so cant comment on the condition of it, but it wasn't memorable in a bad way.

The part that will probably take the longest will be getting out of Krakow proper, although on a Sunday shouldn't be so bad.

Oswiecim itself is a small town and you will have no problems,

With a good map or GPS, driving is a good option

Lock your car and do not leave anything tempting visible, that goes for all of Poland