Hello Ikaria,
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.
After I updated the theme Courtyard and WordPress, my logos no longer display correctly. The logo in header is too small and the secondary logo is pixelated and stretched.
Please check my website on your Android or Apple phone. The logo does not display correctly? Please can we fix this. Here is the link: http://countryclub.co.za
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?