Upgrade Opions For Square Fit Sterio?

[squid]

In my last question a member told me I have a square fit stereo which is really helpful - I didn't know. I'm hoping to get some more help if possible as I'm struggling to find answers.

 

I'm not a very confident stereo fitter but I'll give it a go as I do like good sound. I want to replace my square basic 6000 with an aftermarker head unit with DAB (and bluetooth and usb if in budget). Budget dictates I have to live with speakers so I don't need a cutting edge stereo though an improvement of the 6000 a must. Compatability with steering stalk would be useful.

 

Okay, my questions,

what size is the opening. Google image search on double din seems too much. Is it 1 1/2 din?

Also, what do I need on my aftermarket stereo so all speakers get hooked up? Would the connection adaptor will take care of that or do I need a minimim number of channels on the head unit?

My budget is ideally

Edited May 29, 2010 by squid