1) How to slow down the credit rool.
The credit roll displays (or rather paces itself) for the number of seconds defined in the properties for the media FX. Change (increase) the number of seconds in the “Length” box and the credit roll will go slower… then don;t forget to stretch out the event so that it matches the new length you specified within the FX properties
2) Adding narration.
You can record your narration directly into a new audio track on your timeline (look for the “Arm for record” button in the audio track header).