What sat/nav for W163 ML320 build date Dec 2000

[andrew_zaf]

I have a W163 built in December 2000. It has fitted a Audio 10 radio-cassette with 6-stack CD player fitted on back.

1. I am told I cannot retrofit a sat/nav in my W163. Is this correct ?
2. I am told I cannot fit a sat/nav from another Merc 'cause it wont fit? Is this correct?
3. I am told I can only buy an aftermarket kit (eg Blaupunkt) made for Australia ? Is this correct? (I live in Melbourne, Australia).
4. I am told I would upset the electrics of the car if I install another unit. Is this correct?

I will be travelling in the Australian Outback and a sat/nav system is essential so any advice will be extremely grateful.