Basically on friday I'm going to buy a mini itx board and all the rest for my bmw. Now I've read alot into this and have done many searches and I know there are many similar topics, but I would just like clarification on one question I have left that I haven't been able to work out from these postsm and thats the best way to connect the opus to the ignition circuit. I understand how to connect it to the battery and what amps and that to use, its just the conection to the ignition circuit I'm unsure about.

I know I have the options of behind the head unit,
I saw there is the option to run it from the fuse box through one of these: or is that not a good idea?
idealy I would like somethin in the boot, is there anything around where the cd changer would be as it is pre wired for a changer but I haven't got one, just an aux in converter waiting for me to connect something!

Also I currently have a e46 coupe and I'm getting a convertable at the end of the month, will this make it any more difficult/easier to get stuff to the front of the car

Cheers in advance!