Route looks good to me at first glance.
As the (currently) only biker I won't have a problem with doing 4-500km a day, I can deal with 600km in a pinch but I'd prefer not to do it too often. The main problem for me -compared to cars- is range. While most -if not all- cars will be able to cover all proposed daily distances on a single tank I would have to stop for fuel about every 200km. (I can do more, say 260-270 depending on fuel milage, but I start to get antsy for petrol once I go past 200) This would mean stopping every 2 hours or so taking at least 10-15 minutes to refuel and stretch my legs a bit.
If this would mean planning the trip around my limitations I'd much rather gracefully bow out now, rather than be a bother to all the others. Especially since I'd be the only biker.
That's just one suggestion. And I was assuming that at least some people would prefer doing that bit in parts (mainly thinking of bikers).
Concerning the trip back to Germany I'm planning on leaving a day early since I need to swing by my place to pick up the car for the Ringmeet.
I'm either going back to Belgium by boat (Driving to G?teborg, the schedule would have me board at 4 in the morning on thursday), but this also means I would only arrive at the Ringmeet on friday at 7pm or so.
The alternative is to drive the entire way back, but I definitely need to tackle that trip in 2 parts, 1300km in one stretch is just too much.
As for getting to Helsinki in the first place, I saw in the Google doc there are a few other people looking at taking a ferry from Travem?nde (Eye-Q and Bobble iirc?). I'm up for traveling together as that would greatly lower the price for the crossing*. If not I'd probably still go with my original plan of boating to G?teborg, driving to Stockhom and ferrying to Helsinki, but the logistics of that are proving to be more of a hassle than expected. If I could ferry from Tr?vemunde straight to Helsinki for the same price as my alternative (about ?3-400) I'd much prefer that.
*Not sure if it is possible to book multiple passengers AND multiple vehicles though.