There is no harm in using the same image. But the SEO benefit in the image search on the search engine will be lost.

No point because it's gated.

Off-page SEO of the site needs improvement. Currently, it is in poor state.

Get backlinks from your keywords to the specified page. By this, the specified will start appearing in the SERP.

There can be many reasons for it. Better, provide the URL to reach the exact problem and it's solution. Whatever the problem might be, it can be solved.

User specific run-time interactivity of a web page can be controlled using the Document Object Model. The DOM size should be in-check to keep the web vitals score green.

SEO, Google AdWords, and Facebook Ads will be helpful to fetch traffic on the blog.

You are doing good. Besides these, you should add some unique paragraphs on each such page.

Win good backlinks using blog postings, guest postings, and with other such methods. This will bring good DA to your site.

Google will take care of bad links itself. Regarding the outgoing links from your pages, those must be removed to save the link juice.