The Frozen Star

You start the game in a highly-compact system orbiting a very cold star. Do note that despite its unusually low temperature and mass, Cherra IS a star, and not a brown dwarf, which is thanks to its high metallicity, providing just enough insulation to keep the core hot enough for hydrogen fusion. Though the planets all look easily accessible, it's harder than you think to navigate Cherra's system, as it takes a LOT of delta-V to get anywhere with pure rocket power. Gravity assists will be your friend here, though you may have to chain many of them together, as they aren't as powerful in this system. Everything moves so fast, it's hard to get something to change your trajectory much! Additionally, spheres of influence are very small in this system, so lots of orbital adjustments may be needed to get everything just right.

Cherra is the third star in a trinary system, the Parsec system. As the name implies, the system is only about a single parsec away from the Sun. Cherra is an ultracool dwarf star, however unlike the likes of TRAPPIST-1, Cherra is only kept alight by its extraordinarily high metallicity, being only a mere 59 times the mass of a 1/10 scale Jupiter. Its surface temperature is a mere 1,350 Kelvin, and it is incredibly dim to boot, and as such is roughly on the border between an L9V and a T0V. It is known to have 4 major planets, as well as plenty of more minor bodies inbetween.

The first planet, Pepsol, is 1.04 times the mass of a 1/10 scale Earth, and is incredibly hostile. Ingame, it is a gas giant, but canonically it does have a surface completely covered in a water ocean hot enough to melt lead, which is only kept liquid because it is wrapped under an atmosphere 1,000 times thicker than Kerbin's. It's also noticeably deformed, due to the intense tidal effects of being so close to Cherra while also being so puffy.

The second planet out is Desken, which is 2.1 times the mass of a 1/10 scale Earth. However, because it is also an ocean planet, with the only "land" being a massive ice sheet covering most of its surface, Desken has a relatively hospitable surface gravity. Canonically, it is inhabited by two intelligent colonial species, the Kerbals and the Avali, which is why I highly recommend Tholin's "Avali Space Program" mod for immersion, as it introduces the species into the game. Download it here! https://forum.kerbalspaceprogram.com/topic/207474-112x-avali-space-program/

The third planet, Thorbin, is a whopping 9.3 times the mass of a 1/10 scale Earth. From a distance, it may look like an enticing destination, with visible lakes and oceans, and a thick atmosphere to keep the planet warm despite its distance from Cherra. However, on closer inspection, Thorbin reveals itself to be quite inhospitable, as those wonderful seas are actually made of hydrofluoric and hydrochloric acids, and the atmosphere is a soup of methane, hydrogen fluoride, and hydrogen chloride. Not to mention the high gravity!

The fourth and final planet is Asool, which is 8.1 times the mass of a 1/10 scale Earth. However, it is actually larger than Thorbin, despite its lower mass, due to it having a thick envelope of hydrogen and helium--it is a mini-neptune. It is the only canonically gaseous planet in the Cherra system, and, like Desken, also hosts a small asteroid moon, orbiting closely to its home planet.

Finally, there is the main Parsec system, which is actually a very close binary of Parsec, a B-type subdwarf, and Arcsec, a relatively middling red dwarf. It is visible as a bright white dot from Cherra. This system is in a highly unfinished state, as all of its 4 planets are currently just placeholders.