Testimonials grid using SCSS and BEM

Thanks in advance for the feedback. I'm getting better at this in large part to all of the wonderful help I receive with each project.

Here are a few questions that came to mind:

1. I used multiple scss files for really the first time. I would love to receive some feedback about how that went. Other ways to approach it and so on. (I kind of did what "felt natural" in this case. For a larger project, I imagine I might divide the css differently.)
2. Is there ever a time I would use px instead of rem for the unit? The only thing I could think of is when I set the html font size. (In this project it was 13px.) Should I just keep using rem to my heart's content?

Please let me know about anything you think I can improve upon - BEM, accessibility, anything really. Thanks in advance for the help!