I’m in the described obsessive ultralight packers category, but that’s from years of European travel. So back to the basics:
People on your tour will have 2-wheel, 4-wheel suitcases or a large backpack as their main bag. It’s never been a huge problem to get those from the RS bus to a hotel entrance. The weight of it is something you want to consider - are you comfortable lifting it into the overhead in the airplane, etc.? Also, it’s very important to check your specific airline for their carry on dimensions (and sometimes weight restrictions).
Over many years, my main bag has been a Rick Steves 2-wheel suitcase, then an Eddie Bauer Expedition 2-wheel bag, and the last few years I switched to a Cotapaxi Allpa 35L backpack that I love. (I’m in my 60’s)
During my RS tour last year, I washed underwear and any quick-drying shirt or dress worn that day every night. Otherwise, I washed my pants, etc. during the first night of 2-night stops. That keeps my quantity of dirty clothes very small, so I can switch into something else in the evening if I want a quick late afternoon shower & change clothes after a hot day. I just wash my clothes in the sinks with a piece of Earth Breeze laundry detergent - looks like a dryer sheet, or some hotel shampoo. Wrap it up snuggly for a few minutes in a towel & hang to dry. The RS tours usually have a planned location for some available laundromats, although I’ve never used them. My last RS trip was combined with a 2-week independent trip with my husband, so those clothes were worn for a month. I usually take 1-2 dresses and three shirts & two pants.
Create your own packing list. Use it to do a trial pack of the exact items you’re planning a month ahead. Happy with the results? It can take a couple of iterations before you come to your final packing list. Then this is very important: do your final packing to that packing list. It’s easy for extra “what if” stuff to creep into your bag, otherwise. ; )
If you’re curious about the “weighing the clothes” aspect, I want my backpack bag filled to be no more than 13.5 pounds (I ride a lot of trains and move locations often.). I will weigh several favorite shirts that could be good for a trip on a kitchen scale. It’s easy to shave off some pounds by selecting the lightest weight shirts, pants & dresses. I also bring a lightweight crossbody tote on the plane as my personal item.