If you increase the PR of a page on a site, would that automatically increase home page PR? I don't really care about my homepage because I'm not optimizing that, but because my blogroll is there, people would rather link to a homepage with some PR.
Most probably, all the internal pages will be linked to the home page right? In such case, yes, if you increase the PR of an internal page, then it will pass down the PR juice to the home page.
Each page is ranked independently so it will be where your internal links and external links point to that will help decide which page gets how much PR if any! The age of each page will also add to an increase in PR.
Not necessarily. There might be instances whereby inner page might have higher PR than the home page. However, it will definitely help if you point it back to your homepage to distribute the weight.
Yes, but if you focus on inner page, then your home page PR will be hard to achieve high PR. For example, you get 30PR4 backlink to your inner page, your inner page get PR4 but you get only 1PR4 backlink to your homepage.