Hi Bryan, great work on this overall! I've been looking forward to it since I learned about it at B2C.
I did find something for the errata list-- in the World Generation section on page 91, the Hydrographics step simply has you roll 2D-7 to determine the amount of water on a world, with the only dice modifiers coming from certain atmospheres. Based on the original text, the planet size should also be added to this roll as a modifier.
Thanks!