KSP: Salyut-1
Salyut-1 is the first manned space station on earth orbit, it was designed to fit with Soyuz parts (such as life support and engines) so you don't need to create some kind of space station systems.
Mods: https://github.com/KSP-RO
Wiki:
https://en.wikipedia.org/wiki/Salyut_1
Proton: • KSP: Soyuz 7K-L1 / Zond
Soyuz 7K-OK: • KSP: Soyuz 7K-OK