It is difficult to specify how many "back links", but getting quality back links from high page rank site having different ip address and do follow attributes will help a site to get high page rank.
Some Can Get Even @ 10 Backlinks while high competetion takes like 100-500 PR3+ Backlinks ALso Xrumer Backlinks dont count as Backlinks
It depends on the quality backlinks. It's a plus point if the backlinks are dofollow. Try to build backlinks on high pr sites.
It is difficult to mention the correct number. It all depends upon the quality and ranking of the backlinks.
I think it depends on wayy too many factors to give you an exact answers. Some being the quality of your backlinks, the age of your backlinks, the age of your domain.
there is no criteria to estimate anything like this sometimes pages with 800 back links are at PR4 n sometimes its in millions so it all depend on what is the quality of your page n how unique and qualitative is your content on the page
I saw a stats graph in an ebook which looked like a pyramid. For example to gain PR 4 you need XX backlinks of PR3, XXX of PR2 and XXXX of PR1 but also XXXX of PR0 Edit: But like there was said before me, sometimes you see pages with very small number of backlinks that have a PR4 so maybe there is no correct "formula" for this.
Depends on the backlinks quality,if a page is do follow and got too many links out,then you need huge links.But if there is high PR a do follow page only few links out,then you need not too much,
Get a good key word using Google keyword too, Ad words, Amazon or Clink bank and enough content and you'll surely rank