Is it necessary to go on an organized tour of Girona - if so, any recommendations? Best way to get there? I feel like it's an easy day trip. Is it the kind of place where we can visit museums, stroll and then spend some time at a beach?
It's a very pleasant town. Surely a local guide would have provided much value, but we opted to just stroll about and soak in the ambiance.
Girona is a historic, interesting and very enjoyable city. it is an easy day trip by train from Barcelona, less than one hour trip. It would also be a fine place to visit for a couple of days or more. It is quite a healthy hike from the train station to the old city, I walked both ways but it would have been better to take public transport or a taxi at least one way. No doubt a guided tour would add information and understanding, and facilitate logistics, at a cost, but you give up a lot of flexibility in poking around at your own pace. Girona itself is not on the coast, so there is no local beach.
I do not think you need a guide in Girona unless you have a special interest to feed. For me the highlights were walking the wall, exploring the rather large historic district, visiting the two cathedrals (both with English audioguides, I believe), and seeing the quite-good museum. I spent multiple nights there, using Girona as a base for a trip to Cadaques. It's also convenient for visiting Besalu.