I'm only using this: RTG(stock) (x3), Gigantor XL Solar Array(Stock) (x4) (never unfolded), PPD-12 Cupola Module(stock), Science Laboratory (Idle all the time), 3.75m "Aegletes 2" Nuclear Reactor, 3.75m Electric Generator, 3.75m Antimatter Reactor, Advanced S.A.S. Module, Large (Stock) (x3), 3.75m Alcubierre Drive, Huge Heat Radiator (x4). total weight is around 133t which can be lifted in a single rocket, if you know how to design big lifters, another option could be using docking ports and assembly in orbit. Give me 2 minutes and I'll link a video showing how i transfered from LKO to Laythe(Jool) EDIT: no i did not use any advanced aero breaking techniques or any other magic, simple use of how orbiting works.