It is a drop down menu, you can change it to something that isn't mosaic.
All games offered by Better Repack come with everything released by the developer, there is nothing needed outside Better Repack to make a game complete.
Not necessarily, most of these are likely already in Better Repack. As for how to know, there's no easy way, basically relying on if a warning is displayed when loading the character is the only way I know and the warnings don't give much info, making it extremely difficult to identify a mod. Also, when there is a warning, most times it is because there is a different version of the mod applied to the card than what is already in the Mods folder. The mod has to be the exact same version on both to not get a warning.