Could you try disabling the posts instead of deleting them entirely?  If things take a turn for the worse you could always enable them again and look into improving the posts instead.

<title>Awesome Cool Headline<title></p> <p><H1>Awesome Cool Headline<H1></p> <p>This looks correct.  Then use H2 for subheadings.  The title won't get printed on the page so "Awesome Cool Headline" will only show once on the page content.</p></title>

Is there a way to find blogs with a high domain authority that are in a specified niche?

For example is their a tool that finds high domain authority blogs that focus on tech?

Like others have mentioned you should only have one H1.  This should appear on the page before any other headings such as h2, h3 etc.

The styling shouldn't matter so the h1 doesn't need to be in a larger font size than the h2's.