It sounds perfectly doable to me: I count 7 countries you want to visit, and then it depends a bit on where in Germany you start the first day and end the last day. Two nights in one place is mostly fine. On some of the legs, there are not many daily trains though, so that adds some constraints. There are no night trains in the Baltic countries, but especially the Finnish ones are nice (I’m partial but confirmed by others). You could take a ferry shortcut Stockholm-Turku (Viking Line or Tallink) or Umeå-Vaasa (Wasaline’s carbon neutral ferry), especially if you don’t take night trains up to northern Sweden and down to southern Finland.
This year is a special occasion in northern Finland though, because sometime around Midsummer a train route (by VR) is starting that crosses the twin-city border from Haparanda, Sweden to Tornio, Finland (continuing to Kemi). Also, Oulu is this year’s European capital of culture so you may want to stop by.
To save some time in the Baltics, I might not stay overnight in Tallinn (with the frequent Tallink ferries over, it’s basically a twin city of Helsinki, which is also not huge) and instead continue to Tartu or Riga. Then the train to Vilnius runs only once per day, but from there you could travel through Poland back to Germany even in a single day if need be.
Regarding smaller Swedish towns, check out Lund. It would be a suitable place from which to make day trips in the Malmö region and again, Copenhagen is a twin city (connected by Öresundståg Lund-Malmö-Copenhagen). The section Germany-Denmark-Malmö-Stockholm is known as a bottleneck at times with overcrowded trains and cancellations, but when you get to the Malmö area you can relax a bit as there’s the alternative route to Stockholm via Gothenburg (perhaps worth a visit too!).
It sounds perfectly doable to me: I count 7 countries you want to visit, and then it depends a bit on where in Germany you start the first day and end the last day. Two nights in one place is mostly fine. On some of the legs, there are not many daily trains though, so that adds some constraints. There are no night trains in the Baltic countries, but especially the Finnish ones are nice (I’m partial but confirmed by others). You could take a ferry shortcut Stockholm-Turku (Viking Line or Tallink) or Umeå-Vaasa (Wasaline’s carbon neutral ferry), especially if you don’t take night trains up to northern Sweden and down to southern Finland.
This year is a special occasion in northern Finland though, because sometime around Midsummer a train route (by VR) is starting that crosses the twin-city border from Haparanda, Sweden to Tornio, Finland (continuing to Kemi). Also, Oulu is this year’s European capital of culture so you may want to stop by.
To save some time in the Baltics, I might not stay overnight in Tallinn (with the frequent Tallink ferries over, it’s basically a twin city of Helsinki, which is also not huge) and instead continue to Tartu or Riga. Then the train to Vilnius runs only once per day, but from there you could travel through Poland back to Germany even in a single day if need be.
Regarding smaller Swedish towns, check out Lund. It would be a suitable place from which to make day trips in the Malmö region and again, Copenhagen is a twin city (connected by Öresundståg Lund-Malmö-Copenhagen). The section Germany-Denmark-Malmö-Stockholm is known as a bottleneck at times with overcrowded trains and cancellations, but when you get to the Malmö area you can relax a bit as there’s the alternative route to Stockholm via Gothenburg (perhaps worth a visit too!).