I think these articles will answer a few of your questions when it comes to your AUX port and backup camera/Android Auto... is super helpful and very straightforward...used it to install a backup camera myself in my E60.
https://bmwrepairguide.com/bmw-e60-idrive-upgrade/
https://bmwrepairguide.com/bmw-auxil...-installation/
As far as the sound system I'm afraid I can't help you there, but maybe someone else can give you a hand.