I know what you mean, about not feeling like something's really finished...I'm very shy about posting original work, maybe because of this. But I typically start at the beginning and write until I get a different inspiration--then I stop working on the first thing for awhile, and hopefully I come back to it again...usually, I know what the ending is but not always how I'm going to get there.

Plus, even for oneshots I usually think about the overall plot arc, because I often get ideas for sequels that I'm never sure if I'm going to write...

And I hate rewriting--I've gotten better at editing, but if something really isn't working I just leave it alone for awhile.

Absolutely, the hardest part is the bit right before the end, when one's initial inspiration is already written, the logical conclusion is within sight, but one is still stuck in the build-up...

(Sorry for the rambling.)