Hotel costs can be very different, even if you choose no luxery and just pick a hotel wih "normal comfort". Can you specify what you mean with "normal comfort"? It may be obvious to you, but people do have different views. For some people it is important that the room is ensuite (with your own bathroom, so to speak), have wifi and a comfortable bed. Others may be happy as long as they get a room and if breakfast is included.
Do you have any budget for the hotel?
What we would recommend you to see and do, it really depends on what you would like to do. What's the point in recommending museums if you are not into museums at all? This was just an example. Stockholm can also be expensive, so you maybe are looking for free attractions? And so on. Let us know more about you, what you are looking for and what you want to see and do while you are here.
Budget can really depend on what you eat as well, and if you are planning to enjoy the nightlife and so on.