A couple of basic questions related to SEO.

1)
If I have a site that has several different niches that I am trying to promote from. Example Web Developer broke down into section of Web Design, Graphic Design, Programming, Software for SEO purposes, would it be better to use subdomains for these main sections or use the main domain with a folder like structure?

2)
Is PR different for each page of a domain or ever page has a PR of the same on that domain? Also do sub-domains have a different PR?

3)
When entering a hugely over saturated niche such as web-design, is it even possible to compete with the big sites that have been ranked on google #1 page for years?

4)
Lastly, I have read about how important titles, link anchors, and headings are for SEO and how content is the most important. So left's say we are building a standard header, body, sidebar, footer page. In the the actual markup, would it be better to make sure the main content comes before the sidebar on the page or does this probably not make a difference?

5)
I seen mentioned in another answer here that microformats can help with SEO, is there any fact behind this?

Thank you for any info on this