Boughene: Technology allows production for a very manageable population
Yes, and...
Pretty much everyone's in that space station, per canon.
There's a rule in FFW that you can't just walk into and occupy a planet with an atmosphere -- but Boughene doesn't have a breathable one, and the station where everyone lives may as well be Size 0 ATM 0. To reconcile this, I posit that there are Food Mines on Boughene itself. Fusion-guns excavated massive tunnels that are normally used for agriculture, but if necessary can be a refuge from invading forces.
On the other hand and to put it mildly, Boughene doesn't have a hospitable biosphere. Even at the tunnel depths of the Food Mines, you aren't going to find usable topsoil. Much of the production there is still industrial (hydroponics and carniculture vats, as with the ones on the station) but there is indeed actual farming with imported earth. Oh, and the IMTU version of Boughene orbits the gas giant Komesh along with the other moons Disco Inferno and Donna Summerland. Plenty of space to get down and dirty.... you can dig it.
Wait, how can they import enough dirt to make a difference for the needs of 600,000 people? Easy -- free shipping! The station is at least 2.4 million Td just for living space (staterooms), let alone Ag modules, warehouse space by the docks, and shipyard facilities -- and it's modular. With each module having a 40-year service life, at the very least 5000Td of modules need to be replaced per month, from factories on Efate. Many of these are mostly void space, such as warehouse modules, docking bays, shopping malls, and so forth. These can be loaded up with good dirt from Efate, and thus can take advantage of the stranded cost of shipping the empty space in those big boxes. Cheap grav shuttles bring the dirt down to the mines and there you go. They've been doing it for a couple of centuries so far -- that's a lot of dirt.
Kind of like how the white sands of Waikiki Beach actually came from Manhattan Beach, CA (no, really!)
Trexalon and Collace: Technology, technology, technology.
Yes, indeed. Collace really doesn't have that high a population density per square km (fair sized planet, not ocean-dominated) but the agriculture sector didn't want to give up its vast bio-domes so everyone gets packed into arcologies anyhow.
Trexalon... I have issues with that place that only
start with the Tech Level (couldn't have rolled high enough on a D6 with the available DMs to get it). Still, its low HYD stat means they have to technology their way to sustainability. Well that and being a gas giant's satellite means they've got to roll their own planetary magnetic field or live underground anyhow...