For the Ventrian articles, the main querystring key is 'articleId'. This is what you should enter to link your tags to individual articles on the Ventrian page.
You could, theoretically, add 'currentPage' as a second-level querystring key, and this would allow you to tag individual pages with individual tags, but I would think this is overkill. You really just want to link a particular article with a tag, I can't foresee a use case where you would want to tag an individual page, unless you have a very large number of pages and need to drill down to partway through an article. So unless this is the case, I would leave it at 'articleId'.
Yes, you should create a separate page tag cloud module for each instance of the Ventrian module. By design, the tags on that page will only be shown from the set of tags for either the individual article (when showing the article) or all articles on that page (when showing the article list, ie, when no articleId is in the Url).
If you want to completely separate the tags, you can use the tag categories feature, whereby you create a tag category for each separate page tag cloud instance - ie news, library, blog. It is then possible to configure tag lists and tag clouds to only show tags from that category, if you wish to do so. This wold then require three separate tag list pages - one for each category.
The usual case is to just to have a page tag control on each separate page, and then to have all the tags mixed together at the portal tag cloud level (showing all tags across all articles) and then showing all blogs, library entries and news articles mixed together in a page list. But you can separate it out if that's what you want to do. I hope that is not too confusing, unfortunately tagging is an area where confusion is the norm because of the loose connections and inter-relationships.