I enjoyed this tour in June and also did a trip report.
I'm not sure where you are from but I'd prepare for wet and cool weather. I live in N. Idaho and can usually manage most temperatures with a SS tee and a waterproof jacket ( a must for this tour - NOT water resistant, NOT a poncho, NOT an umbrella) but also wore a long sleeve Dri-fit top or sweater parts of all days on our June trip. I actually wore glove liners on the day we did Mull and Iona as it was quite chilly with wind and rain.
Which hotel does your tour use in Edinburgh?
Loved the National Museum of Scotland which is so big that you can visit more than once if you have the time. Our walking tour of Edinburgh ended up there so I went in then and then another time on independent days after the tour ended. I had on the list but did not get to Rosslyn Chapel, the Botanical Gardens, the HMS Britannia and the National Museum of Art.
If either you or your travel partner are in to gardens, consider skipping the building at Cawdor Castle and spending all your time in the gardens. We did the house/castle first and yes, it was interesting but WOW the gardens blew our collective socks off!
Have a wonderful time!