DC cable installation method is pretty standard around the world I assume. 

I'd be careful about such assumptions - the physics may be common but local standards and practice can certainly vary. In France for instance the norm for buried AC cables seems to be to use plain sheathed cabled in plastic ducting often with no Earth at all, whereas in the UK the normal practice is to use cabled with a solidly earthed armour, so that hazardous cable damage will likely result in a L-E fault and rapid disconnection.

Depth is usually a matter of local conditions - deep enough so it's unlikely to be disturbed or damaged by heavy vehicles passing over, shallow enough not to be too much of a pain to trench or collide with deeper services (main sewers etc). There may be local standards for various types of underground services to minimise contention - e.g. for roads and similar locations in the UK - http://streetworks.org.uk/wp-content/uploads/V1-Positioning-Colour-Coding-Issue-8.pdf

Soil conditions (and local ambient temperatures) might need some consideration too - UK/N. European assumptions about soil dampness and thermal conductivity might not hold true in the in the more arid parts down under for example. Generally though, DC cable ratings seem to follow single phase AC ones (although at 1000A you'd be off the bottom of most common table ratings tables).

Separation wise, the ideal would be far enough apart that the cables didn't influence each other thermally (exact numbers would very with soil conditions etc) - but that's not always practical, especially if all the cables have to meet up at some common source.

  - Andy.

Thank you very much, Andy. This is awesome. 

For clarification, is it 1000V or 1000A?  You have both in the question.

For clarification, is it 1000V or 1000A?  You have both in the question.

1000V, David.