How many times we can use this H tags in single page - H1,H2,H3,H4,H5,H6

On my blog's main page all of my titles are H2 or 3 and they all seem to rank very well. I've also added other H tags within the post and I get plenty traffic. From what I've experienced a few per post would be fine, not sure about more than that though.

Well you should only have one h1 tag per page other than that there is some flexability.

You might want to read these articles for some info on how to best use H tags.