Arles is absolutely wonderful but it is on right now so I think it is going to be tricky to get there! The actual exhibitions are on for some time, but all the fun happens in the opening week; parties, openings, meeting, talks and the film and slide shows in the Ampitheatre each evening. I couldn't make it this year due to moving studios, so I will be calling some friends who are there soon to get a report. If you go next year, book a hotel well in advance, months in advance, maybe even a year in advance. Sadly the train, which is a great way to get there is usually a lot more expensive than Ryanair to Nimes.
All the best