So basic rule number 3 is: Retire at a place you personally like. For me, that is Gotland, at least for now.
I will not give you an in-depth description of Gotland here. Wikipedia is much better at that. Let me just say that Gotland is Sweden’s largest island. It lies in the Baltic sea, about 100 kilometers off the Swedish coast and on a similar latitude as Gothenburg. The climate is similar to Southern Sweden but slightly sunnier. So summer temperatures are slightly above room temperature, and winter temperatures some degrees below freezing. The number of daylight hours varies greatly, between 18 hours in summer and just 6 and a half hours in winter. That makes for very distinct seasons, which I enjoy. I even started to see the beauty in the long, dark winters.
Gotland has a long history and was inhabited since the Stone Age. Its largest city Visby was shaped by its medieval history, where it was an important member of the Hanseatic League. No less than 10 church ruins can be visited in Visby, which I find very charming. Although Gotland has only 58.000 inhabitants (24.500 in Visby), is has a rather large infrastructure including a campus of Uppsala University.
And then there is the sea of course. Gotland has an 800-kilometer coastline with some narrow beaches and interesting stone formations called rauk. Gotland has a smaller sister island, Fårö, to the North. It has only about 500 permanent inhabitants and some of the nicest landscape.
Are there any disadvantages? Yes of course, but few. Gotland is quite remote. It can be reached by ferry from Oskarshamn and Nynäshamn, which takes a bit over three hours. There are also flights from Visby to Stockholm.
Also, while distinct seasons are nice and all, but the winters could certainly be a bit warmer and brighter. The sea could be warm all year round. But all-in-all, I consider Gotland a great place to live. I see a big advantage of staying in Sweden, where I know the culture and the language. It is relatively close to friends and family in Sweden and Northern Europe.