Just got back from this trip (may 12-June 1) and it was the best 3 weeks of my life. First time traveler so I had some of the same questions as you, although I'm male and I shared a room with my sister on the tour the whole time, so I can't help you with the solo part.
Did I feel like I was on the bus a lot?
Never. After some of those long days (and nights) the bus rides were mostly a welcome sight where I could relax, catch up on some sleep, rest my feet, learn about the next place on the tour, etc.
Did I get enough ground time, walking?
Absolutely. Amsterdam and Rome I was dead after walking so much. I never got the feeling of being "cooped up" or anything like that. In fact, most of the bigger cities you'll want to take the metro/bus to get around because it's a nightmare to try and walk back to the hotels.
Hotels were good, always centrally located and most of them had air conditioning. The ones that didn't I think you had to go down to the desk and ask them if they had it or not because sometimes you will think you have it on but it's not really on until someone down there "unlocks" it for you. But that was only like 2 places. If you're a light sleeper, earplugs are a necessity. Since the rooms might be a little (or a lot) warmer in August as compared to May, your window(s) will likely be open all the time, in which street noise can be a hindrance to some. (Thank goodness I sleep like a rock)
Also wifi in the hotels is usually good, only a few the signal wasn't very good in our room. Just be aware most of them have passwords and such.
Something I didn't know before the trip. Almost everyone on my tour either had been in Europe on their own or with family/friends somewhere prior to the tour, or extended their time in Europe after the tour was over. I think only like 6-7 of the 28 of us actually left Paris for the states after the tour was officially over. Don't know if you have time or money to do something like that, but I wish I had. After gaining several travel skills along the tour, many people booked extra nights in Paris in order to go to Versailles, see more of Paris, etc. Some had rail passes and left to go to other places in Europe, and a few extended on to do 2-5 days in London or something like that. Now that I'm back I really wished I would have sucked it up and gotten more days in Europe out of my airline ticket! So if you have that freedom I would highly encourage you to do so.
Otherwise, you'll have an absolute blast on this tour. You'll learn so much and just be amazed at some of the things you eat, see, and do. Hope some of this helps you! Happy travels!