My theory on why Zod wanted Lois on the ship was that he could tell Kal-el had feelings for her, and that he figured as long as she was safely off the world he might agree to their plan of killing all the humans to make room for the Kryptonians.
However Zod never presented that angle. It seemed more like Zod may have tried to learn the truth of how Clark had been raised from Lois, but even that was less than clear.
On the issue with "why do they have to terraform earth", my first reaction is, terraforming won't overcome the planet not being in the right orbit. Still, I would have to agree it is an issue that was not really adequately dealt with.
