A bit late, but partly based on my own experience: I’ve done Gdańsk – Vilnius – Rīga – Tallinn – Rīga – Klaipėda, single driver, albeit I did the trip in summer. From Gdańsk onwards is an educated guess based on map data.
There’s an overnight ferry from Stockholm to Tallinn vie Mariehamn. An itinerary would look like this:
- Tallinn – Rīga (about 4 hours)
- Rīga – Kaunas (about 4–5 hours)
- Kaunas – Gdańsk (about 8 hours)
- Gdańsk – Rostock (about 7–8 hours)
- Rostock – København (via ferry Rostock – Gedser, about 3 hours driving, 1 hour on the ferry plus 1 hour for check-in)
- København – Stockholm (via Øresund bridge, about 7–8 hours)
If you squeeze this into two weeks, including the two surrounding weekends, and depart from Stockholm Friday evening, you can add up to four extra days to your itinerary. You could, for instance, add a day in Helsinki or one in Vilnius (which is about an hour from Kaunas and, since there’s a motorway from Panevėžys to Vilnius, takes about the same time from Rīga). Or, once you are in Gdańsk, you could consider Gdynia and Sopot as well.
From my own experience, Gdańsk–Kaunas was the most stressful part of the trip. Most of it is along DK16, which goes through villages and is quite narrow, with a bunch of trucks, which cuts down on your average speed. (Do note that I did this leg in 2011 and, as far as I remember, there was no expressway from Elbląg to Ostróda then). Plan plenty of time for that. The same might be true for the Gdańsk–Rostock leg.