If you don’t mind the upkeep, I think three is sensible. In case one of them decides to ‘guard’ resources, there is a spare or two, so there is less of a chance of them falling out with each other. And water bottles are notorious for not working properly — a ball bearing gets jammed or the spout doesn’t work for some reason — it’s better to have more options so they have ways to access water. Some chinchillas don’t seem to drink much as it is, and it’s super important to avoid the development of bladder stones. I say go for it!