Will inform of routes when it is time for it.
As indicated in another thread best way coming from south is from Västervik - Visby via
http://gotlandsbaten.seSince it lowseason early June timetable fits much better with departure around noon friday the 2nd,
From Oskarshamn the ferry will leave 9pm, 21:00 and it is the only one..
EDIT:
Keep calm with accomodations reservations. Plan the ride but bookingsites and etc. will open after eastern next year.
During winter they will have vacations, maintenance and set prices for the next season. Therefor they don't want bookings with old prices. You will now only find that no hostels are availble in the moment.
Sweden is a large country with plenty of room. Less stress than in middle europe. Relax and things will solve, when meeting is it is still low season. Finding hostels during weekdays don't even need pre-book like campsites, cabins, youth hostels, B&B