I have a 2012 Alhambra Lux with a reversing camera. I would really like to have CarPlay thought and it would seem a common approach is to order an RCD 330 from AliExpress. There seems to be some confusion around reversing cameras though, it comes with a cable to hook a camera up but I don't know whether I need some sort of RGB -> composite converter (the RCD 330 has a composite camera input)

Anyone know what sort of camera mine would be?

A factory VW camera will be a non standard, proprietary connection. You wont be able to interface it into a generic head unit as easily as just plugging something in.