Yes a variety is must for search engines like heading tags, bold text and some images with Alt tags.
However for reading point of view a starting line and an ending line is a must and should be good
It will really help be more appealing to readers and search engines if you add some variety to the formatting. So for example, some tables, bullet points, headings of different sizes, etc. Hope that helps!
This one strictly depends on the topic you are writing about. Think like a user who is googling the query you are targeting in your article.I want to know, what should be SEO friendly format while writing article like should we use table of contents, how many H2,H3 etc
I want to know, what should be SEO friendly format while writing article like should we use table of contents, how many H2,H3 etc