You should check out some of the worlds I'm generating in My Traveller Universe Sol Subsector. By the way Malenfant, I based it on your 3-d star map. It is not a cannonical Traveller sector, I just started with the Star data and let the dice roll. I used the Stars Unlimited program to generate the initial UPP, then I used the system generating Data to generate the Moons around the Main World, the gas giants and where they are, and the asteroid belts. All I list about the other planets are their sizes and their diameter in kilometers.. I've also randomely determined the rotation rates of the main worlds, and their orbital period duration in years. You can look at them and see if you find any silly nonsense results. The tech Level of Earth in this campaign is B. F is the highest tech level in the sector. I've also determined the size of the size zero worlds, at least the one with the Starport on it.
The social data is rather arbitrary. As for why a garden world would have 3 people on it, perhaps humans would find the wildlife to be rather unpleasant, maybe the climate is unbearably humid and hot, maybe the planet is swampy and the air is filled with nasty biting insects that spread diseases or are venomous. The ground could be squishy and filled with poisonous critters, and giant carnovourous monsters, the day length could be unbearably long for humans, such as 80 hours for instance, and just one parsec away could be an asteroid belt with 10 billion people.
The first thing that must be remembered is that asteroid belts have way more surface area than any single planet, it is easier to burrow into an asteroid than into a planet due to the lack of gravity. Once enscounced in an asteroid, the humans can set their day length to whatever they want, the air temperature inside could be set and a constant 72 degrees with just the right amount of humidity.
A perfectly habitable planet is basically one where you can breath their air unassisted and walk around on the surface without a space suit, this perfectly habitable planet can still be a rather unpleasant place to live. What if the gravity is 1 1/8th times Earth's gravity, is a size 9 world, has an 80 hour day, is hot and tropical full of biting insects and is swampy. The planet has no continents and instead the land area is broken up into millions of islands seperated by stretches of water filled with carnivourous sea creatures, some of which are venoumous. All sorts of creepies and crawlies inhabit the island, they bite and they sting. Lots of slithering reptiles with poisonous fangs. Flowers whose pollen causes hallucinations and allergic reactions in some people. There are no deserts, and high levels of rainfall across most of the planet 60% of the time. Now tell me, would you rather live here than in an air conditioned cave dug out of an asteroid?