Re: So did land plants exist in the Cambrian (which you said did not earlier)?
As for the issue of animals, dont forget that Cambrian LAND-strata is very very rare and precious. It might not be correct to assume that no evolution happened on land in Cambrians times. The is no guarantee that the most "advanced" creatures (all assumed to be watery) survived Cambrian times and left descendants. We should not assume that there were no land animals in the Cambrian times.
Actually, in my country we can. No plant or animal fossils have been found in the Vanrhynsdorp Group (Early Cambrian in age) or any other Groups (Klipheuwel, Nama) or Subgroups (Kansa) deposited during the Cambrian in my country. My country missed complex life in the Cambrian!