Every minute of finished video usually requires several minutes of decision-making, trimming, and review. Beginners often see a 6:1 or higher ratio; experienced editors get closer to 2-3:1.
Generally yes — lock the picture (story, pacing, cuts) first. Doing color or heavy audio work before the cut is finalized means redoing work when scenes change.
Build reusable templates (intros, lower thirds, color presets, audio chains) so you're not rebuilding the same setup on every project.