The Netherlands is built for arriving by train with a bag you do not want to drag over cobbles for four hours before check-in. NS trains drop you in the middle of Amsterdam, Utrecht, Rotterdam, The Hague. Hotels often will not take the bag until mid-afternoon. Stations are busy. Hostels have lockers of their own, until they do not. The simple move is to park the suitcase for the day and walk, which is what the city is for.
Radical Storage is a network of shops and hotels that take luggage by the day, including around Amsterdam’s centre and other Dutch cities. It sounds like a gadget. It is the difference between seeing a museum and touring a station. You can also use hotel luggage rooms if you are staying there that night. The point is not to pay for a product. The point is not to spend the first afternoon as a pack animal.
After the bag is still, the country is small enough that a second city is a morning. Amsterdam is the famous canal ring and the crowd that comes with it. Haarlem, Leiden and Utrecht are short rides and a different density. Bikes are not a tourist activity; they are how people commute, and they will not slow down for you in the marked lane. Dutch is the language. English is so widely spoken in the cities that visitors forget to notice. Cards work; cash is rare. The weather is wind and drizzle even in months that look green on Instagram. Give Amsterdam a couple of nights, then use the timetable. The canals were never the whole country, they were just the part that photographed first.