Aim for 150–300 words. Include your main keyword in the first 2–3 sentences for SEO. The first 157 characters appear in search results.
Yes — timestamps improve viewer experience, can appear as chapter markers in YouTube search, and signal to the algorithm that your video has structured content.
YouTube recommends 3–5 relevant hashtags. Adding more than 15 causes YouTube to ignore all hashtags. Place them at the end of the description.