1. It would be more convenient to look for accommodation in Sopot or Gdańsk, if options in Gdynia are too limited. The festival shuttle bus takes you to Gdynia Main Station, from where you can take a train to Sopot or Gdansk. The train is called SKM and runs quite often (I think they add more trains at night during the festival). When looking for the accommodation in Gdanks or Sopot, try to get something near one of the SKM stations (https://en.m.wikipedia.org/wiki/List_of_SKM_stops). Kosakowo and Rewa are on the opposite side of the coast and while there are some city buses running from/to festival, they are very limited, especially at night.
2. Hard to say, maybe still this month, but they usually close their line-up as late as in June and since there are only around 12 international acts still to be announced, they can wait with the next drop till April.
3. I'm pretty sure VIP passes dont give you the opportunity to get closer to the Main Stage (at least they didn't in the past). Can't see them on their website either so maybe you're right that they are sold out.