I read somewhere that the site title in the home page should be H1. I would like to know whether the site title in the post pages should be h1 or h2 or h3 or whatever, since there is already one h1 in the post page(i,e post heading)
Heading tags are a way of organizing and prioritizing content in a HTML document. There are 6 heading tags - H1(the most important one) to H6(the lease important one). Among these six tags,H1 tag is the most important tag followed by H2, H3 and so on. By default Blogger uses H1 tags for the blog title, H3 for post titles and H2for sidebar titles. Having proper weighted headings is really important from an SEO perspective and this tutorial will help you to assign heading tags based on importance.
Generally, the heading tags contain the keywords can be found in Title tag as well, this way your on-page optimization would look good, however, title should have broad keywords, it can target more than those keywords which are in heading as well..