Hi Genomicus,
The steps I described assumed your hypothesis was that significant evolutionary steps are carried out by designing the necessary DNA and then inserting it into the reproductive cells of existing lifeforms on Earth. This would, of course, be a labor intensive effort requiring continuous activity (including up through the present) that would leave behind a great deal of evidence.
The steps you described seem more consistent with a hypothesis that the first life was designed, manufactured and seeded on to Earth, and that evolution took over after that. The possibility that life was seeded here from somewhere else is already an accepted hypothesis, but your hypothesis introduces the additional idea that it was designed and manufactured rather than natural.
This raises the obvious conundrum that if the origin of life on Earth required a designer, then the origin of life on the designer's home planet also required a designer, and the origin of life on the designer's designer's home planet also required a designer, and so forth
ad infinitum. To break the conundrum one must accept that although Earth lacks the necessary qualities for abiogenesis, there must have been at least one planet where life arose naturally, and that life on one of these planets must be the ultimate origin of life here.
But why do you believe life couldn't have arisen naturally here on Earth, but could have arisen naturally elsewhere? There must be a compelling reason to believe this (and interstellar travel, too) in order to justify the amount of intellectual effort it would take to understand the details of your proposal.
It just seems to me that before discussing how many fairies can dance on the head of a pin, one must have a compelling reason for believing fairies exist.
--Percy