No matter what, for SEO it always helps to have your exact Keyword/Keyword Phrase on each page within all three tags (H1, H2, and H3). You should also have your Keyword/Keyword Phrase three other ways which is BOLD, UNDERLINE, and ITALIC on each and every page of your website. Doing this alone will help to boost your SEO and SERP results greatly. -James
Stuffing your keywords in all 3 will most likely not look natural and could be considered keyword stuffing. Just add the keywords naturally throughout the page, but most likely you will want to have your phrase or some variation of it at least in the h1 tag.
HTML does have custom sizes defined. H1 being largest and H6 being smallest. You can make use of CSS to put a custom size and style to each one of these heading tags so that is not a worry. Search engines consider H1 - H3 to be important.
yes it has I mean H1 tag will always enlarge your text size but you can control it via different fonts in CSS..
Yes each tag has the unique functionality.. Use your Main keyword in H1 tag (with or without extra words) ; Try to keep the “Keyword†at first. Use H2 tags to break down the main topic: you can find a way to write SEO effective and still reader friendly H1, H2 tags. Just use H3 tags with the natural flow of the article to make it more reader friendly. Ignore it if it is not needed. Do not use H4, H5…… tags just because you want better SEOed page. They don’t carry much importance anyways.
Mostly H1 (heading 1) tag used to being title large and H3 (heading 3) tag is used to being title small than H1 tag.