What to change and what to keep

I am about to do worldbuilding for the version of Sweden that will be the setting  for at least two series. It will involve a lot of research. From history to folklore to administration. Not to mention deciding how much history changes. Do I keep everything and just adds  magic? Or do I keep somethings and change other?  I honestly don’t know. What I do know is that I am keeping the locations of the major cities, though I might change their names. We will see.

I am going to do my best to not buy too many books. Instead I am going to visit a lot of museums and download relevant articles from Riksantikvarieämbetet and Riksarkivet.

I am looking forward to this. It will be fun!