Thanks for your questions. Here are the answers to your questions.
1. In the case of changing the content, basic knowledge of HTML will be helpful but you must have basic knowledge of React too.
2. HTML template builds with HTML markup language and React JS version build with React JS. They are different frontend technologies.
3. Some main reasons to go for the React version are Faster loading speed than HTML, modular design approach, complete separation from backend in case of using an API.
4. We didn’t try it on a windows server, but it works fine on an apache server. It should work on windows server too.
5. The CRA (create react app) framework or the default framework has disadvantages in terms of SEO compared to the HTML because of client-side rendering. But react framework like Gatsby, NextJS uses server-side rendering approach which overcomes those disadvantages.
6. If you have knowledge about reactjs, you can add new pages to any react template.
I hope the questions are answered.