1. We have an issue with logo (will be fixed within 24 hours with theme update) while importing via demo importer. You can simply fix your logo issue by setting secondary logo image and then again remove it(Set for temporary).
2. Hero Slider Image size of 1920x1080px will be perfect.
Could you please remove the secondary logo image and save the customizer value. Now refresh the customizer and upload the secondary logo again and save the value. Let us know this resolve your issue or not?