I'd definitely stay in Haarlem, as it's so close to the bulb fields and you can rent a car and drive around easily. Besides, it's a nice little city with lots of nice places to eat and stay. We lived there until a year ago and I'd be glad to make suggestions.
Definitely go to the flower auction. It's amazing. Be sure and get there very early, as Rick suggests.
I'd also definitely make a trip to Kinderdijk and to Zaanse Schans, to see the windmills. Kinderdijk is a Unesco World Heritage site, but it's often overlooked on tours. It's a beautiful area and you'll be glad you went.
Driving up and across the enclosing dyke and then down the coastline to the pretty villages of Hindeloopen and Makkum will show you the side of Holland that you always hoped to see... It's beautiful. Hoorne is also a lovely place.
As far as history goes, you could go to Leiden to the Pilgrim's Museum. If you're in Haarlem, don't miss the Corrie ten Boom House. There's a little bit of preaching that goes with it, but it's a fascinating story about how the Dutch handled themselves during WWII. Have a wonderful trip. Linda