I hope you have booked a hotel. Then you can ask your hotel to help you contact a tour agent. Or you can search for one on TripAdvisor. People there are all very kind and helpful and they work well as tour agents. Websites are not permitted in answers here but you can try googl ing "visitazores" Good luck to your trip.

I do not think it will be a big problem for someone with mild vertigo. The view point at the start of the trail is probably as close as you will come to looking down over the edge. Recommend you wear good shoes and bring a hiking stick for support. Also it can be windy / cool so a light windbreaker is a good idea plus water and sunscreen too. The walking itself is not to strenuous. Hope this is helpful. It is worth the effort. :)

You can see it all with Bruno from Toboga Azores! Look him up! He took us absolutely everywhere in one day on Faial ... Because that was all we had! It's worth it if you can get him! Best guide around and dirt cheap!

There is none that I am aware of .. Best to stay in Horta. I recommend hotel du canal

Hi... best is just to go if you have a hire car. Otherwise, I believe you can quite reasonably get a taxi to take you. Personally, if staying at a hotel, I'm sure they will help, and no doubt know someone who takes small groups up to the Caldeira. You will love it, as long as the weather is clear! Enjoy.