Start with Google Search Console to see what you already rank for and where the impressions are. Use Keyword Planner for ranges. Use AnswerThePublic + ChatGPT for question expansions. Use Bing Webmaster Tools to confirm volume estimates. Skip the paid tools until you have outgrown the free workflow.
Marginally. The free tier is limited to a few searches per day, and the data is licensed/older. For free, the combination above is stronger.
Surprisingly yes for ideation and question phrasing. Bad for accurate volumes — always verify with a real tool.
Usually yes once you cross 200+ pages or do competitive analysis regularly. Ahrefs or Semrush are the standards.
Google Search Console + a habit of monthly review. Most teams ignore it; the data is gold.