It's not possible to estimate the needed efforts in this way - more important then the number of sheets and objects will be how the datamodel look like and supports the requirred gui-calculations, how the sheets and objects should be look like and at last but not the least - your experience with qlik sense.
It totally depends on your data model and the requirements.
If you know the data is in right format and you can get all the requirements then UI will not be a big deal.
I would start by checking whether you can get all the requirements with the existing data model. If you can't get all the requirements then estimate how long it will take for you to sort the data depending on how good you are with the scripting.