Great response Aitch! I don't have much to add - but will add my personal stamp on this real quick
1.When I link my blog, do I use the url of my domain or the url of the page I want to rank?
The idea is to create blog posts with relevant content that contain links to each page on your site that has value.
Once you get to #1 you don't need to keep linking as much and can focus on boosting other pages that need to be linked
2.How many blogs should I post the same article in?
If you post in the BU Blogs the articles/post content needs to be at least 30% different than anything you have posted.
It's in your best interest to make each post the best it can be with related keywords so you get more of a relevance boost.
3.What’s the difference between a regular blog and an announcement blog?
BU Blogs are called "announvement blogs" because we use them to announce our URL's
4.If I contribute an article to the member’s blogs is it supposed to be originals only or can it be a modified PLR?
Originals are always best - at the very least add a few extra sentences and make your post contain related keywords.