As far as I'm concerned, the point of a first draft is to get your basic idea down onto paper. The purpose of revision is to spot the strengths and themes of that work, amplify the strengths, prune the weaknesses, and rearrange whatever needs to be rearranged.
At this point, I would say to NEVER underestimate the revision process. I just added the best 1500 words that I've ever written to my novel, all in the name of revision. Quite honestly, I could not have thought of what I just did without the basic work being under my fingers.
So while writing your NaNovel, don't be determined to get everything right. You don't need to do that. Get what you can knowing that you are always stuck with revisions.
Also, don't get stuck with linearity. If you are ready to write a section, then write it. If you like starting with the end, then start with the end. If you like to write lots of snippets, then assemble them, then do that. It's the rare human that can sit down at a typewrite and bang out a story, page 1 to page end, in one draft, and call it a publication. Even Clemens couldn't do that. And look at Shakespeare, he kept refining his plays through his entire career. So do what makes sense for you and have no shame about it. idiosyncracity rules!