Nice is great. I’d stay in the old town. (La Petite Maison is an institution for a fun dinner & Le Plongoir is gorgeous for dinner with a view) and then perhaps a night or two in Cannes - it’s a great place to base yourself if you want to be amongst the buzz. I’d also try to do a Provençal vineyard half day if you have time. Just an hour out of town is the most beautiful landscape and old French chateaus!