One of ACKS' default assumptions, which I've commented on before, is that of the "failing empire", with barbarians at the borders and corruption within. Another of ACKS' standard assumptions it the inland sea, typically modeled after the Mediterranean in Antiquity. But there's another perfectly good inland sea in Europe that gets a lot less attention: the Baltic.
Which, it turns out, is probably a fine model area-of-operations for a DaneACKS campaign. Much more so than the North Sea, with its super-long travel distances and terrible weather. The water-area of the Baltic is about 330 24-mile hexes, which is about a quarter of a 30x40 24-mile hex mapsheet, leaving plenty of room for surrounding lands.
One problem(?) with the Baltic as an ACKS setting is that Scandinavia and environs are, historically, not particularly well-populated. At all. In 1570, already somewhat after our target era, the population density of Sweden was only about 5.2 people per square mile, while that of Finland in 1550 was a mere 2.3 people per square mile. At 300,000 people in an area of 130,666 square miles, you're looking at 60,000 families spread over (roughly) 4 30x40 mapsheets of 6-mile hexes. In 1150, estimates (since at that time there was certainly no census, nor a centralized state to conduct one) place the total population of Finland between 20,000 and 40,000 people, or at most 8,000 families, giving a population density of about 0.3 people per square mile, which in ACKS terms suggests a handful of class VI markets over that entire area. Which is... rough, for adventuring and supply. The rest of the Baltic isn't much better; Gdansk in the 1100s had a population somewhere between 1000 and 2000, which is a class V market. Many of the population centers currently on the Baltic map above weren't even founded until Christianization hit, and population records for pre-Christian settlements (like Forsigtuna, the pre-Christian capital of Sweden) are basically nonexistent. So... I guess there'd be room for some "creative license". On the plus side, such a setting does play very nicely with tribes as the autonomous domain unit, which would be fun.