1) yes it is a great improvement
2) mine do because the car is too low nd they hit the chassis on hard turns
3) the Hotchkiss cost me $350 delivered from l-tunedparts they are adjustable as the Eibach but stiffer (150% compared to OEM)
4) yes it is a must with lowered suspension
They are really easy to install, took me 1 hour to fit both, just get some WD40 on the bolts before.
Hotchkiss ones come with new bushes and grease flagon