How to use a presentation with sound in Storyline (optimal)

Hello partners in crime (Instructional designers, e-learning specialists and Articulate lovers),

I'd like to ask you to think about the best approach.

I recorded a presentation where a SME presented with MS PowerPoint on video. I recorded the session on tape and now also have the audio track separated from the video. The video is only interesting from the welcome and close. . The other slides are actually better in MS powerPoint, so I want to have a combination.

I extracted the audio track and have it now available as an MP3.

I want to accomplish to have the module in Storyline. Can I import the slides, start (video) and end (video) on separate slides and still use a single MP3 file? Or do I need to cut the MP3 files as well?

or ...

Is it a better approach to set the sound in PowerPoint first and then import everything?

Any first thoughts?