A deep dive once a month is recommended to stay ahead of trends. However, "comment mining" should be a weekly habit to catch specific audience pain points as they arise.
No. While tools like Semrush or Ahrefs are powerful, you can do 90% of effective research using YouTube search, Google Trends, and manual competitor analysis as outlined in this plan.
The "Sweet Spot" is a topic with high search demand (people are looking for it), moderate to low competition, and a high relevance to your specific expertise or niche.