i just downloaded db last night on ps3 if i choose to go to solstheim can i return to skyrim whenever i want to or do i need to complete the story there before i can i dont want to be stuck out there if i find it too difficulkt at first im starting with as lower level warrior and dont want to wait to build up

You can travel back and forth, there's no restriction that I'm aware of or found.

You only have to pay for the first visit, after that a character can Fast travel between Solsthiem and Skyrim.
Ninja'd.