Sounds like a great adventure!
First off, I'd mention how "short" those distances are per day (not in a bad way). To me, that means you are really ideally set up to carry your own "luggage" in panniers and could do the whole loop with no support or added expense. Pretty much all hotels are going to allow a luggage drop or a luggage hold, so you can very easily ride from Hotel A - Hotel B, drop the pannier, and continue with exploration by bike, foot, sailboat, canoe, etc.. Riding from Amsterdam to Haarlem will be under a 2 hour meander at <10mph, so if you're riding that bit in the AM, you end up with midday into late afternoon wide open for other exploration. Only the Gouda to Amsterdam day looks VERY long compared to other legs of the trip, so maybe consider a stay in between those two stops (or realize that ~50 miles is a nice challenge day!). Aalsmeer is about halfway, and it might offer the opportunity to add the sailing bit you mention. Boat rentals seem relatively common in the Netherlands, but sailboats a little less so. If not Aalsmeer, maybe Sloterplas in western Amsterdam is an option (and we've seen sailing elsewhere on rides in the countryside like outside Delft).
Haarlem to Leiden presents a perfect day for the "beach", so I would definitely make sure your route runs along the coast for that bit.
You will also get to ride ferries - big and small - and they can be a real fun time. We really loved the hand-operated one we encountered outside Delft where I shared the crank spinning duties with a Dutch family to pull our little ferry across a canal. Other ferries had a nominal fee (1 euro or so), so keep some change handy (never hard to do in Europe). I have to recommend - in Amsterdam - taking the BIG ferries that connect downtown to north Amsterdam (leave behind Centraal station). Free and fun way to get a longer trip on the water.
One general thought is to get familiar with the Dutch knooppunt route marking system that connects the countless cycling routes easily and efficient (and into Belgium and even a little to Germany). I like and use the fietsknoop app and website. Free and straightforward.
The other good rule for all travel these days is to plan museums WELL IN ADVANCE if you want to get a ticket. Not all are swamped, but Summer is high season, so having your timed entry locked up will help you both plan and actually get in to the museums that interest you.
Another rule to live by - STOP EARLY and OFTEN - to snack, stretch, relax, shop, have beers/ice cream, take photos, explore. As I wrote, the distances are SHORT, but for my wife and I add quite a chunk of time to all rides because we are stopping to check things out. For example, we did the Leiden "Cheese Route" loop while staying in Leiden which was a 13 mile loop through some dairy farmland, and one stop was for fresh ice cream from a dairy we rode by and towards the end, cafe sitting to have beer and snacks while people watching. Taking those breaks almost doubles the 1.5 ride time, but is why we enjoy riding vs doing that in a car (or not doing it at all).
What sort of budget are you thinking for hotels? We generally spend a little more on a hotel than some folks but since a dollar goes a long way still, it never seems extravagant (compared to "normal" US chain hotel pricing). Also, are you going to spend a few days at the beginning or end in Amsterdam? I would definitely home base there for a few days. And what about general attitudes about what to see beyond the bicycles? Museum interests? Historical areas? Food?
And a final mention of using Dutch Bike Tours as a planning tool. They've got routes and loops you can look at as a good way to craft your own plans.
