1. If you are using one continuous bibliography for multiple documents it is probably best to manually control them. You can drag and drop bibliographic references from Zotero into Word, and you can use a shortcut key (look at the shortcut section of your preferences to see all the shortcut commands) to copy the intext citations or footnotes to your clipboard and then paste them into your documents. With this approach you will not get the added benefit of the Word plug-in, which will keep track of each item you have cited and place them in the bibliography automatically, but you will be able to have much more direct control over how the items are placed in your document.

2. Yes, open your library, click Ctrl+A (Command+A on a Mac) to select all the items in your library and then right click on the selected items and chose "Create bibliography from selected items".