1. Script insertion is easy! There are literally available fields on any node of dialog that are labeled for scripting, ie: Script that fires when conversation ends, script that fires if conversation aborts - these two are on the root node of your convo. After that each node has a Script that determines availability and a Script that fires when spoken field.
Into these fields, if you have made your nwscript, you would enter the name of your script minus the suffix ( no .ncs ) and that should be about it. Then test your dialog and scripts
2. This is more complicated, essentially you need to record the VO in the correct format, and then follow a very specific naming convention. You will then need to extract .lip files and apply some lipsync to your speakers. There is a tut made just for this question... I suggest you search for it
3. The basic animations of speaking, or combat animations? For stuff like laughing while speaking, shaking your fist, gesturing... that is all done with the DLGEditor. In the lower section of the editor, slightly on the right-hand side, are two boxes, labeled Current Animations (should be empty) and Available Animations. Drag from one box into the other, and that should be about it.
If you want more complex animations, you will need to script an in-game action sequence... you can see something along these lines explained in this thread
Hope this points you in the right directions!