Hi John, we visited Chamonix as part of the RS Eastern France tour in May 2015. We had a free day there and just loved it! Our guide suggested that we get up early and take the first gondola to the Aiguille du Midi. He also suggested that we purchase a day pass for a few dollars more that included some additional sites. The Aiguille du Midi was a spectacular, amazing experience, with terrific views. At the summit be sure to see the "step into the void" skywalk.
After that we walked back to the station and took the train (included in the pass) to Montenvers where there is an ice cave carved out of a glacier. Amazing! Lots of steps but totally worth it!
Chamonix is a small town and I don't think you need a guided tour (as I mentioned, this was our "un-guided" day). Check out the info in the RS book and get a map from your hotel. If you're looking for a restaurant recommendation, we had a wonderful dinner at La Calache - fondue and raclette.
Hope you have a great time!