Hi Tamsin, it sounds like a wonderful hike, and you'll be walking in a very pretty and still rural parts of Catalunya through the comarques of the Gironès, La Garrotxa, and Osona. I'm thinking you'll want to plan 2-3 days for each of your major stops (Girona > Olot > Vic) depending on how fast you walk and how much time you want to spend exploring.
I'm assuming you're following one of the Via Verde routes between Girona and Olot. The route is online:
https://www.viasverdes.com/en/itineraries/itinerario.asp?id=52 (see the "Description" section).
On the route between Girona and Olot, you might consider staying in Sant Feliu de Pallerols, as it's a large enough town to stay and eat, with a pretty river running through. Outside of Sant Feliu, there is a lovely B&B run by a very welcoming couple (he's from Scotland and she's Catalana) called the Rectoria de Sant Miquel de Pineda. The rooms are comfortable, and the food is local and excellent. There's a 12th century romanesque church next to the house, and if asked, they'll give you a tour.
I totally agree with
@anamcara about Girona. It's a great, small city. It was very quiet until it became a site for "Game of Thrones" tourism. It's worth exploring the medieval part of the city up high on the hill, the cathedral, and "El Call," the old Jewish quarter.
Please post more to share what you learn about these hikes.
