Where will be performing? Probably somewhere at or near the top of the town? The Cathedral and Park at the very top of the town and grand Piazza is high but lies below those two places.
The streets run uphill from the train station towards the top of the hill. Much of the modern town is flat or relatively gentle but the last few blocks to the top do get steep. Walking one of the streets like Corso Italia on Google maps gives an accurate impression of what the walk is like.
Is this repeated thing? Because you could always get a cab in town to take you to the top of the hill if this isn't a standing three week engagement.
There are escalators from the parking area on the back of hill top. If you are driving this is an option but would otherwise require a bus or something around the town to that area which would undoubtably take longer than just taking a couple blocks at a time and resting.
I don't know if these comparisons help but Arezzo is nothing compared to someplace like Toledo and I think is more manageable than Siena which kind of undulates around and has much more "up and down" walking around than Arezzo. But those last couple of blocks after a long day walking back from the train station did make themselves known.
Sounds like an awesome chance if you can make it work,
=Tod
PS I don't have any news on Rick's condition but he is travelling the country this month and next stumping for his new book so he must be feeling well enough to spend time and energy on promotional events. So that's good news.