That would be, respectively, none of it and all of it. Contrary to popular myth, things like Babylon 5 where an entire series was plotted out meticulously or Jim Butcher's Dresden Files where he had 20 books all mostly plotted, is VERY VERY MUCH the exception to the rule. Most of us are making it up as we go, and even if there's a vague plan, it rarely survives contact with the enemy, as it were, and it changes radically by the time it's executed.I don’t know how much of New Frontier was planned from the start and how much was made up as the series went along, I dare say a good deal of both.
A lot of times you don't want to tie yourselves to a big-ass long-term plan because then Future You is stuck with some dopey-ass idea that Past You had and you have to execute it. Much better to keep it vague.
To give a New Frontier example, when Peter wrote House of Cards, he had no idea what actually happened on the Grissom when Calhoun served there. It was, in essence, a placeholder which would be a springboard for Future Peter to tell a story when the opportunity presented itself. Said opportunity came in the Captain's Table miniseries.