Well, the less I can say is that each time I ask, you provide a lot of informations. Many, many thanks for this.
2....use multimesh instance
Yes, I already saw tuts about this, and it appears one of the best solutions to save resources.
About the other options, I have to search a bit more the pros and cons.
But what is particularily interresting is the procedural spawning. I recently saw a video about this and in case of mining operations (yes, a feature I want to implement), it looks like it is THE solution.
4th part (create a planet texture) of the Blender tutorial completed and available here
Another example of what is possible to do with nodes only. Yet another planet, but I'm a bit proud of this one. Indeed, the first try was... really, really ugly !