Information about Haarlem

The train is very easy to take back to Amsterdam. It's about a 15 minute ride to Amsterdam Centraal.

Not sure what your price point is but I stayed in the Ambassador City Center Hotel with a Rick Steves tour plus a night ahead on my own. I felt it was well-located altho I did pop for a taxi from the train station since it was raining buckets when I arrived. It's right off the Grote Markt and faces the side of St Bavo's Cathedral.

http://www.ambassadorcitycentrehotel.nl/en/

As far as trains between Haarlem and Amsterdam, they are almost continuous, like every 7 1/2 minutes. The trick when traveling from Amsterdam Centraal, is figuring out which trains are going to Haarlem. Since it is a short ways away (15 to 20 minutes), all the trains are passing through on their way to somewhere else, so Haarlem does not show up on the train board. A little research before hand, perusing the printed train list will help. There is an App for that if you have a smart phone, or as a last resort, ask directions;-)

In Netherlands, you generally buy the ticket out of a kiosk, scan your ticket to get to the platform, then after you arrive, scan your ticket to exit the platform area. The whole country is set up like the Paris RER system. Both the entrances and exits have turnstiles to make sure you bought the right ticket. People with passes (most Dutch people) scan in and out and the fare gets automatically deducted from their account.

From Amsterdam Centraal trains to Haarlem leave from track 1 or 2. They can have a variety of destinations, but the intermediate stations are also mentioned on the electronic displays above the platform.
Don't forget to have your ticket at hand when leaving Haarlem or Amsterdam stations. You need it to open the gates.

We're staying four nights at the Lion d'Or in late April. It's recommended by various guidebooks, and right across a square from the station where we can connect to Amsterdam and also the airport. But I don't have first-hand experience to share.