Yes, you need JGR Patchpack, and enable the realistic braking option, and maybe also train speed adaptation
I also recommend the multi aspect signals NewGRF, to show yellow signals when a train is reserving ahead
Does the newGRF change the train behaviour, or just the signal colours?
No, the NewGRF just lets the JGR Patchpack realistic breaking reservations be visible (and only works in JGR patchpack).
Yes, you need JGR Patchpack, and enable the realistic braking option, and maybe also train speed adaptation