I want android auto for sure but with the firmware mod im not sure what to do . The firmware mod here doesnt work for the 4100 correct? I would like to have the built in nav but also have android auto but cant really afford the 7100 or 8100 . If i got a 5100 i can get android auto with the firmware mod you have here correct and then it would have all the features as a 8100/8200 ? Are there any bugs with this firmware mod or things that wouldnt work ? 

on 5x00 / 6x00 will be AA

I thought the 5x00 and 6x00 only has carplay and not android auto?

Only Car Play for 5x00

is it possible to use a blutooth obd2 module with torque on the 4100

no