I loved Amsterdam. We stayed centrally too (9 of us) and could access most things on foot, but you can also buy travel cards for the local buses - we bought ours through the hotel directly and they were reasonably priced.
Our hotel was WestCord City Centre hotel - small but easy to find and great as a central base for the city.
Would hugely recommend a little cafe called Greenwoods Singel for breakfast.
There's loads to see and it's a great place to visit. We did walk through the red light district but I personally found it a bit sleazy, but it's all part of the experience. Easy enough to avoid if you're not keen to visit it.
We found the sex museum hilarious and some of our group went to the Anne Frank museum (but try and book online in advance otherwise you will literally queue for hours with no guarantee of getting in). They do release random tickets online so worth checking daily (the hotel we stayed at had a computer with free access).
There's a great street food market but I can't remember what it was called! I remember it being on the bottom-left of the local tourist map distributed over the whole city.
If you're into cycling then some of our party did a cycling tour and said it was great - but intense - not for new cyclists! Again, I can't be 100% sure of the company's name but it might have been Mike's Bikes.
We also did a fab canal tour through the Lovers Canal Cruise company - they have an office by the Anne Frank house and we booked on the day which meant we were lucky enough to have a boat to ourselves (as they didn't sell any more tickets that day).
If you're into your pubs, there's a cool pub built into a windmill towards the north of the city called Brouwerij't Ij. It takes a bus ride from the city centre unless you're happy to take a long walk there. Definitely get the tourist maps (from hotels or tourist information) because they have all the bus routes.
There's also the NEMO Science Museum which has a really cool rooftop garden with water features and great views of the city. It's worth a visit on a nice day. We didn't visit the actual museum but that I've heard that's good too.
You'll easily fill a trip up with things to do. It's a great place!