Starterquestions
 

Since it is very difficul to get in touch with a gtr i hope to get some answers her.

1) I am in sound competitions (EMMA), so it is very important for me to know if there is the possibility to replace the soundsystem. Speakers should be no problem, but the headunit seems to complete integrated. Can I bypass the complete oem headunit?

2) Since i am getting (my wife) a child ... can i fix a child car seat in the back?

It doesn't seem like the GTR is the car for you. Why not purchase a 4 door car with a less complicated electronics set up. Why spend all that money on a GTR, just to rip out the internals and have a kid throw his juice on the floor? Have you ever been on the inside of a minivan after kids have been in it for a couple of years?

I don't know about the sound system, but as far as child seats are concerned, yes, you can fit child seats in the back of a GT-R. I wouldn't use it as my primary family car, but it can certainly get baby from point A to point B while the minivan is getting serviced.

Good luck.