1. I wanted to change a logo so I just googled "high resolution nintendo logo" and used that. Rename to match the file name in the folder and overwrite with the one you downloaded
2. Anything that came up MD in Big Box for me, i went back into LaunchBox, right clicked the cover, edit and then deleted all the MD images that were downloaded. Went back into big box, don't know if you have to but I went into Options and refreshed all images and then the Genesis version now appears.
3. Can't answer that
4. You need to download game play video. For testing purposes I got my at EmuMovies. Once downloaded I renamed to match the console name..ex "Super Nintendo Entertainment System.mp4" and then I dropped into Launchbox > Videos > Platforms. If the videos still don't play try going into BigBox options and changing the video player from VLC to Windows Media Player. Worked for me.