As per android docs, java 1.8 is only supported by API 24+ (Android 7.0+). The bigger market share is under that version.
It is not necessary, nothing is never necessary xD, but it helps to run the project without any configuration or IDE requirement, and ensures that the gradle configs are well configured.
Well… I cloned the project and imported it to intellij, tried to execute it and only got errors. So, I didn’t go further, not that interested (I’m just commenting this things because it can be the difference between the community adopting a tool or just leaving it die with the time)