"Do not think about what they do with all the sewage."
You're hitting the "Coruscant Limit"
From the comic:
"You'd need to import the entire output of 10,000 agricultural planets to feed them...80,000 Super Star Destroyers delivering fresh produce every day!"
"Do not think about what they do with all the sewage."
Of course, Coruscant does not have 80,000 Super Star Destroyers delivering every day. So, at some point, Anakin will realize what they actually do with all the sewage.
"Have some Soylent Green, Anakin. At least this stuff is made from people!"
In "Ringworld," the city-covered home planet of the Puppeteers was supported by five agricultural worlds. Maybe Niven didn't want to go there. They moved their world further from their sun to avoid heat dissipation issues.