Hi, Dawn: Pam might have meant me, although she hasn’t asked me to respond yet.
We did this tour in early May, and had a great time. However, we took the tram from the bus station to the tour hotel area. (We stayed at a different hotel pre-tour, but in the same area, near St Anthony’s Basilica.)
I think walking would be perfectly safe and reasonable; whether or not it is “smart” would depend on the weather, how tired you are, and how much luggage you have!
I second Pam’s suggestions of the Basilica, Scrovegni Chapel (if you can still get tickets; they sell out quickly,) and the Botanical Gardens. We also enjoyed a great MC Escher exhibit at the Centro Culturale San Gaetano.
We also made our own visit to the Palazzo della Ragione, and we were glad we did, because the city tour with the group did not include it, much to our surprise.
This was our second time to take this tour, so I can say with reasonable confidence that you’re going to have a great time.