Sure, you can leave it blank. Or noindex/nofollow the page if you don't even want Google to consider it.
Check this out from Backlinko: http://backlinko.com/on-page-seo You want to get the write title, h1 tags, and make sure everything is centered around a topic that's relevant for searchers. Focus on your visitors, not Google bots.
It's the tags in the header of the webpage. Allows you to control the Title, keywords, and description for search engines. They index these tags then use them in the SERPs
Yes offcause, your On-Page is Must stronger then off-page. If your on page is not good or not sensible you can't get great results. you must update on-page.