Yes of course bold keywords really very helpful in effective SEO. Today's almost expert use such techniques.
Is this ok.....let's say we write a post about movies, and our keyword is The Dark Knight so we bold it 3 times in the article, but then we also bold other movies we mention. We may bold Avatar once and Spider-Man once as well as Lord of the Rings. Is that ok? We usually bold all actor names and film titles
The search engine spiders will consider all tags with in a post to try and work out the quality of a readers experience. As with keywords this is very easy to get wrong and quite difficult to balance and get right.
The <h1> tag is very important. I think that is the basic in SEO. And most people take for granted this. You will let Google find your content easier through the <h1> tag.