1. on our demo, we use image with 1920×1080 size. i personally say its the best option. because it will fit almost on all device size. also keep your image size bellow 150kb.
2. what is that mean? you don’t see those comment box? or you only see 1 input box on your comment section?
3. click on toggle toolbar, it will show you the third row. toggle tool bar is on the first row, placed on last icon.
4. yes WordPress restrict you to upload “weird” file. you can use alternative upload option like using dropbox, or google drive to host your file.
5. our menu using gradient color. you can use PNG. its like a transparent image.