Numsgil-
I'm afraid all those were around long before the cambrian explosion, except for number 1: that might have contributed.
But even bacteria can use sexrepro, while eukaryotes, which were around long before the cambrian explosion, all are diploid and use sexrepro. Multicellularity appeared in the precambrian, in the form of ediacaran biota. However, something turned one of those ediacaran things into the first bilaterian, and after that, life had a foundation to make all known complex organisms.
So, I don't know if that works out. One idea I heard was the emergence of advanced predators- in a world of a. minimalis, there emerged a quickdraw. This didn't kill off everything, but left an area where there were very few plants, similar to moonfisher's nnbot evosim. This is where intelligent/interesting behavior evolves, and as these dead zones grew, life inside the dead zones had to evolve in a way similar to bots in the IBBleague. So, basically we need a huge sim and need to wait a huge amount of time.
ikke-
what do you mean by "have algea and animals follow separate evolutionary steps for instance by different (contradictory) metabolism genes." Do you mean to make sure that sexrepro offspring of the algae and animals will not be viable?