Do you have to have completed the regular main quest in order to go to Solstheim, and participate in the other new quests there? I hope it's not true, as for example, what about those of us who would rather bring an ordinary character that is not the Dragonborn to Solstheim?

No however some dialogue will be different depending on whether you have or not

I am sure you can go there without doing the MQ of Skyrim. What I am not sure about is what you would do once you go there, with regards to the DB MQ.......

Like CCNA said. Skyrim's world is open whether or not you do the MQ, except a place like The Blades headquarters, so getting to Solstheim should be unrestricted to access.

For the quest you probably have to at least be aware that your character is the Dragonborn.

You might have had to do dragon rising cause the quest starts when you are attacked for being the fake dragonborn hard to do if you are not dragonborn

no plan on starting new character since been away from skyrim in few months and i read you dont need main quest to be finished to start dragonborn

tes series motto is "freedom''...how they can force you to complete the main quest ? ask this to yourself next time, even more because we are tired to see that same "creative" question for the 10000 time

You are always Dragonborn. It's in your blood.

AND YOUR SOUL SOUL OF A DRAGON... YAY i just tried writing sentences in CAPS and its FUN!!

From what I've heard, no, you don't have to finish the Main Quest.

I, however, plan on going through it with my main who has finished it.

Some dialogue with Miraak changes depending on whether or not you have defeated Alduin.