I was on this tour in mid-May 2019. It was a colder, wetter than usual spring, even the locals were complaining. To answer your questions:
1) Although I was in pretty good shape for riding my horse and mucking stalls, I was not in as good of walking shape as I should have been. I worked up to 3 miles including hills. What I didn't do enough of were stairs. So my prep for South of France tour in 2022, I walked 3 miles a day, adding 150-200 stairs up and down. I also added Zumba, stretching exercises learned in physical therapy for my back and weight lifting. This combo worked great. This year I did the same without Zumba but because some meds were off, I didn't do quite as good as last year. I'm now prepping for September 2024, going back to 2022 routine. Takeaway: Work on stairs, you will encounter a lot. Edit: thought I should add that I was 68 and DIL was 71 when we did SofI. I’m turning 73 soon.
2) I used everything I packed: 3 leggings, 7 shirts, 5 sets undies. What I wished I had packed was an extra sweater. It was cool enough that I wore my cashmere cardigan almost every day. An extra sweater would have allowed drying time so I could wash mine. I took a lightweight jacket. I don't have to worry about rain in AZ so only took throwaway rain coats. Not a good choice. Too light. I bought a good packable rain poncho in Sorrento and still travel with it.
An extension cord was handy, some hotels had out of the way plugs. Now I travel with face masks, covid tests and thermometer.
To save weight, I now take and wear one pair of walking shoes and pack a pair of walking sandals. The extra pair of cute walking shoes didn't get worn enough to warrant the weight/bulk. Because I have problem feet, I take silicone toe protectors and BandAid blister bandaids. I do hand wash on the first night of a two night stay, so pack folding hangers and laundry soap sheets or Forever New powder. I'm changing to solid shampoo to save 311 bag space. Dramamine is a lifesaver on bus days and any boat rides.
3) I researched and booked our independent days pre- and post-tour. I assigned tour research to my sister-in-law, but that didn't happen so we winged it. I now travel solo so being organized is very important. I research tour free time, buying tickets when needed. I also preplan independent time pre- and post-tour, about two weeks total. I don't take guidebooks or pages; I don't want the added weight, almost everything is online and I haven't needed to refer to them.
It's a great tour. You will have so much fun.