I have aftermarket signals on my bike and one side does flash faster than the other. It’s not a cause for concern.
Your brake light should come on no matter which brake you use.
Is the bike jerking when you downshift because you’re going too fast for that gear? Feathering the throttle as you let out the clutch will make for a smoother downshift.
Having a Kawasaki mechanic go over it will be money well spent.