Sorry, not going with you but I did this tour a few years ago. It is spectacular. Really. I had so much fun and am still friends with many of my tour mates after several years. Another RS guide told me he went along as an assistant guide once and was so impressed that there were blockbuster sights every single day!
-DO look up the cities where you will have free time and have some idea of what you might like to do. The guide might mention something you hadn't thought of but you'll have more fun if you research.
-When you go in to Venice, plan to take just a change of clothes, pjs and some toiletries in a day bag and leave your suitcase in the bus luggage compartment. The bridges in Venice are actually steps and it's a PIA to pull a roller thru the city plus it's a pain to get them on and off the vaporettos. I rearranged when we left Reutte and put my stuff in one of my packing cubes and put it in my bus bag.
-Consider doing the same thing for Monterosso al Mare. The bus will park in Levanto and you'll take the local train to Monterosso, then walk to the hotel. This is not as difficult as Venice.
-If the guide offers any extra activities, DO it! My guide had a couple of extra dinners (he paid and we paid him back), the gondola ride in Venice, an excursion up the Schilthorn in Switzerland as well as some hiking in the afternoon (transportation in Switzerland is expensive but just bite the bullet and do it!).
-I hope you are spending a day or two ahead of the tour in Haarlem. My regret is that I didn't allow enough time to see this city.
-Have a bus bag which you can leave on the bus during the day. Guide book, kindle/iPad, snacks, water, rain jacket, corkscrew, hahahaha!!
-The bus driver will usually have water at 1€ each. Ours also had beer and wine and maybe some soda. You generally put a hash mark by your name and settle up as you head in to Paris.
-Be sure to sit with the bus driver at some of the meals. They are such interesting people and I love the way they are included as part of the group on Rick's tours! Richard often drives the 21 day tour and he is fabulous!
-Do some kind of journaling every day. REally. You think you will remember but this tour moves fast and you'll see SO MUCH stuff that you'll have better memories if you at least make some quick notes every night.
-I hope you both have waterproof jackets. Not water resistant. You'll want to continue touring in all weather!
Have an excellent time!