Coilovers for fiesta mk6 5dr 2004plt.?

if i get coil-overs do i need to change the shock absorbers? i currently have 17inch kei rims and 35mm lowering springs on. i wanna slam the car as much as possible before the wheels rub, approx 50- 60mm. any advise when lowering a car and what else i mite have to do. thanks :)|||GRRRRRRR