We imported the audio track in the exact same way as we imported the video clip. When editing an audio clip the tracks will appear on the bottom few rows, they look like this. The top of the 3 is the main (default) audio track, the picture of the speaker in the top left corner is to toggle the mute option. We used this for all of the audio sections of the video clips we wanted silent. We then dragged the audio into the second lane labelled "Audio 2" and muted that lane.
When we needed captions in between frames rather than editing them on premiere pro, we decided to create them on photoshop and import them as image files