Always film roll away with your clips
even if you don't use a whole lot of it
it doesn't hurt to have it there.

Even in the editor I've been using
sometimes it cuts it like a mili second short, starting to see it in my videos.
If I'm lacking roll away there is a pause in the clip at the end.
Might help.

As for the quality thing, try different formats when rendering.
Some of them will surprise you.