actually, for the Yeerks, I don't think they would mind if it took years because they certainly didn't have the number of Yeerks to take humans.
As for the assault on China, wouldn't you want to build the Kandrona rays before you infest so many people? other than that your plan sounds pretty good. It might be a logistical holocaust, but still good.
Your plan brings up an interesting alternative... use Hork-Bajir and Taxxons as a diversion. And have the humans come running for protection to a new world governent...control led by the Yeerks. So use HB and Tx to drive the humans into the Yeerk's hands.
