I did a similar trip during the summer of 2016 - ended up being one of the best trips of my life!
I crossed from Harwich to the Hook of Holland and rode a similar route to your plan, up through Germany and Denmark, across 'the bridge' (the famous one from the
TV series).
From there, my original plan was to enter Sweden and head for Gothenburg and then on to Oslo in Norway. However, due to roadworks in northern Germany, I though I was around a day behind, so I headed straight up to Stockholm instead. Then I just continued north until I arrived at the Arctic Circle.
Staying in cabins is a great idea as they cost around €20 a night and give you a warm dry place to stay and hotels can be costly (I was quoted €175 for a night near Nordkapp!) and you don't always want to pitch a tent after a day's ride.
When I arrived at Nordkapp, it was 23°C and I was told by the car park attendant that she'd never seen a day like that up there.
I headed back south through Finland towards the ferry crossing from Helsinki to Tallinn in Estonia. I would have liked to cross over into Russia to visit St Petersburg but didn't have time before I left to sort out the visa. The ferry from Helsinki to Tallinn was €100 for the night crossing which included a cabin and, even though we docked at around midnight, they let you sleep on the ferry until the next morning, saving you the trouble of finding somewhere to stay that late at night.
Your plan goes further south than I travelled as, from Estonia, I just rode west through Latvia, Lithuania and Poland. My final day was a mad dash as I had to get back for my sister's 50th birthday. I woke up in Poland, had lunch in Berlin and was back at the ferry port in Holland with 15 minutes to spare before they closed the gates!
A wonderful trip of 4,500 miles (plus another 500 up to my sisters and back for the weekend) over 10 days.
Regarding the bike: you'll need something that gets good mileage. The further north you go, the fewer petrol stations there seem to be... or maybe I missed them! Coming down through northern Finland, I went 300 miles between petrol stations and was so glad that I had an extra gallon strapped to the back (which I used twice during the trip). Because of this I would suggest using the GS 800 BMW which is very frugal or the Tiger 800, as I did, which returned around 55 mpg for the whole trip: that was 4,500 miles, fully loaded with panniers and a top box, having fun in the twisties and the 90 mph all day dash on the last day.
Oh... and cruise control was very welcome!
too much to choose from and not enough money 
