Sanjoaninas is the largest festival on the island of Terceira. This year it will be held between June 22-July 2. Because of this, I would certainly spend 5-7 days on Sao Miguel, and stay in a Ponta Delgada hotel only. There is no need to book a hotel in Furnas. Then fly to Terceira and stay in Angra do Heroismo for the rest of the time during the feast.
Yes, my guide includes driving tours and walking tours for all the islands. You could easily spend and entire summer in the Azores and not see and do everything, especially having nine islands from which to choose.
I have been suggesting to everyone who contacts me with specific plans, to book your rental cars first (book one with free cancellation, just in case), then book your hotels (again with free cancellation), and lastly book your flights. Car rates this past summer saw daily rates in the $300.00 range for a small car in Sao Miguel. Supply and demand is limited on all the islands. Do not procrastinate with these logistics. The longer you wait, the more you will pay.
Make restaurant reservations at least three days before. If you can make them even earlier, that is optimal. It was a challenge for my family to get somewhere to eat at without either a three hour wait or being told they are fully booked. I learned my lesson! This was in July and August, 2022..
Tourism has gone through the roof in the Azores since my first trip in 1994. My subsequent trips (over a dozen) since then see more and more Europeans discovering the Azores. Lately, Americans and Canadians add to these numbers.
Ferries between the islands is not what it used to be. There has not been any ferry service between Sao Miguel and Santa Maria for years. The service between Faial, Pico, and Sao Jorge remains rear round and dependable.
The only issue with inter-island flights any time during the year is due to inclement weather. Otherwise, SATA is dependable and probably the only means of transportation.
Certainly read the Freemium portion of my guide to get you started. It is in the post written by the webmaster at the top of this Portugal Forum. Yes, it is free! I am currently in the process of editing the guide to become a Second Edition, but it will still be a few more months until it is ready. The current guide has plenty to keep you busy.
Whether or not you decide to download the full version, please know you can contact me with any questions, ideas, or concerns.