No idea if anyone has tried this but it has me curious.

When starting a New Game, what is the earliest one can go to Solstheim? More importantly, can one go early on and not get thrown into the main "Dragonborn" quest line?

I'm asking because I am going to start a new game soon and really wanted the new Rune spells that the Tel Vani guy offers.

My big concern is that I do not want to trigger the Dragonborn quest too soon.

Can you go to Solstheim without triggering that quest?

As long as you don't visit the Gbeards in the MQ, the Dragonborn quest won't start.

Correct, and I plan to use that fact for future characters.