Hopefully what I know of these things are correct, but obviously correct me if I'm wrong.
Preload adjusters- Let's you adjust your spring preload in your forks to match your weight (just like our rear preload). Basically to set your front sag while at rest. I have preload adjusters and I believe they're adjustable from 5mm-20mm with clipons.
Emulators- Used to mimic cartridge forks that most supersports come stock. They're used to set rebound dampening and compression dampening (how quickly the spring will bounce back). It's a way to have a plush ride while still being firm (think going over bumps).
Springs- Changing springs will either soften or stiffen the front (depending on what you need because of your weight). Ninja 250 has pretty average springs that will dive for many people so stiffer springs or progressive springs will help.
Oil- Also will help stiffen or soften the front.
I have preload adjusters and 15W fork oil installed and do feel how the front suspension needs help since I installed the GSXR shock. Without an emulator, going over a bump will either be harsh or soft, but cornering will be firm or wallow respectively. The goal is to have the front and back rebound and compress at the same rate. With a stock 250 shock, you can only adjust preload so I wouldn't think an emulator would be necessary. I liked having it at 5 to have firm cornering, but obviously most bumps were jarring for me since I weigh about 160. I'm trying to dial in the GSXR's shock to match my front to avoid having to get an emulator. Hope this helps
