Hiya mate, if ya get standard nissan shocks you wont be able to go lower than 40mm with the lowering springs (about £100), as they'll just destroy the shocks. i went 40mm with nissan shocks and was fine.
The alternative is to buy an uprated shocks/springs set, which cost about £200-250 and you can go to about 70mm i think?
After that you need to invest in some coilovers! (£500+)
Its up to you which you go for, and mostly which you can afford
but needforspeed.co.uk have a pretty good selection!
Hope that helps