I messaged CamScanner, and they explained that the paid app ($1.99) is enough for the needs I described them.

The premium account ($4.99/month) includes everything the paid app has plus some, but is geared towards a specific type of user, not just for general needs.

Thanks all!

p.s. regarding Google Drive, I've occasionally had focus issues, but retried and it went through fine. Suspect the issue may be your camera.