This is entirely based on what you want to gain from Amsterdam, but I’d say 3 nights and 4 days is a decent amount of time for a city break, however, you could definitely achieve what you want in less or more
What not to do should be the question! Depending on your budget for Amsterdam, there will be things you may want to skip or miss out, but since I did Amsterdam on a budget, I’ll take you through my itinerary as an example!