Squeezing more out of the Ultimate Solar System

Squeezing more out of the Ultimate Solar System: Some Ideas.

* Increase the mass/luminosity of the parent star. This allows the giant planets of the same mass to have larger hill spheres, and thus fit in more moons.

* Add an extra orbit inferior to and superior to the habitable zone, and the only terrestrial planets and moons should be desert planets (with underground water or sparse lakes, preferably). Give the inner planets high albedos and the outer planets lower albedos. Desert planets have more stable climates. They're less likely to turn greenhouse and less likely to turn snowball.

* 3:2 resonant moons. Another way to get more moons in the hill sphere of each giant planet. 3:4 resonance may work as well if the moons are small enough.

* Increase the mass of the giant planets. Not too much or you raise the roche limit up too far as well as cook the inner moons. (No matter what we do, the inner two or so moons will probably be cooked by tidal volcanism)

* Trojan moons. The gas giant planets are definitely 25 times more massive than the moons. Therefore, each gas giant moon's orbit can have two mutual Trojans instead of a single moon.

* Heiarchal Quadruples as trojans. These are the sun-orbiting co-orbital binary planets and the giant's trojan binary planets in Type I and Type II respectively. This may not be practical for the inner system without a star that's too luminous to support long life. But for the outer habitable zone at least, it is possible to put a close-together binary in a large orbit around a second close-together binary. Therefore there's 4 planets in a single satellite system and 8 on an orbit. The more luminous star helps a lot here.

* Trojan moons of Super-Earth trojans. In the inner system, a different strategy could work to get in six worlds instead of four on an orbit in Type I. (However you have to space out the planets more in Type I, so this will probably be used as the trojans for the giant planets) The parent planet will have a mass of 9.9 Earth masses, just enough to keep it from being a Neptune. The moons will be co-orbital trojans, of 0.198 Earth masses. This is just barely enough to let them remain stable as Trojans according to the 25x mass rule.

* Laythes as solitary, dual, triple, or quadruple moons of superior Giant Planets. Add more giant planets after the outer Desert orbit, up to the system's Frost Line. Give the moons thick, greenhouse atmospheres. These moons will be close to their planets, and cooked by tides. In this case this is a good thing. The moons would be covered in ice, but the volcanism has heated them up to liquid water temperatures and the greenhouse effect will keep the heat from being lost to space. Energy at the frost line will be hard to come by, and these planets will probably only be inhabited by chemosynthetic extremophiles near volcanic vents, but at least they could make reasonably good colony locations. The Trojans of these planets shall be binaries with relatively eccentric orbits (maybe even with interesting spin locks) to increase tidal activity to cook them as well. Kerbal Space Program's Laythe, a cold gas giant's moon that is covered in liquid water, is the namesake for this type of planet.

Options for the other moons of the cold Jupiters:
* Europas. Make these planets water worlds with ice crusts, kept warm on the inside by tidal heating. Not a human-habitable planet, but there could be life here at least.
* Greenhouse worlds. Kept at human-habitable temperatures but more or less geologically inactive. No power source for life beyond the frost line still, and life will have a tough time even inferior to the frost line.
* More Laythes, but on eccentric orbits. This may cause some stability issues for the system, but it allows more geologically active moons.

Alternate use of orbits beyond the habitable zone but closer than the frost line: other biochemical habitable zones.
* High temp/low temp, biochemistry, approximate distance from Sun.
* 500C/400C, Fluorosilicone-Fluorosilicone (0.1au)
* 445C/113C, Fluorocarbon-Sulfur (0.1au-0.6au)
* 100C/0C, Protein-Water (0.95au-1.35au)
* -33.4C/-77.7C, Protein-Ammonia (1.5au-2.1au)
* -161.6C/-183.6C, Polylipid-Methane (5.9au-15au)
* -240C/-253C, Polylipid-Hydrogen (20+ au)

These may result in very alien life and non-human-habitable planets, but Mesklin wasn't habitable and it was an interesting place to explore! There's still plenty of stories to be told with alien planets that are living but deadly, and I dare say it adds some variety to the mix.