There doesn’t seem to be much information online regarding where to stay in Ceuse. We ended up renting an AirBnB in Saint Laurent (neighborhood of Sigoyer). This does involve driving to the crag. If you want to stay within walking distance, I would recommend searching around Les Guerins (the actual campsite). Les Roses and Les Bonnets are also close enough for walking.
We flew into Nice, due to the flight price. Time wise, Marseilles or Grenoble are closer though.
For supplies, we found the supermarket in Tallard to be adequate. While it’s purported to be expensive, it was more enjoyable than trying to drive in/around Gap.
For rest days, the lake near Embrun is quite enjoyable.