well having recently lowered mine by 40mm by meself on me drive the small bit of advice i can give is get ready to get new bump stops as both mine on either rear side were totally knackered and split in two, and also get ready to be screaming at it!

I have fk dampers and springs all round, bought from a guy on ebay for bargain price of £150 brand new and hes from errr austria or belgium and they're brand new. At first i was a bit disappointed but having now been to demon tweaks and got the camber, castor and tracking all checked and adjusted and now the suspension is actually softening up Im really pleased with it. Handles a lot better you dont have that major tilt on corners and just feels more sollid.
The fact your car is 30mm lower already shouldnt play a factor cause you're replacing everything but in terms of looks wise, if you go for 40mm its only gonna be cms difference looks wise but obv newer kit. If that makes sense.
if you're doing it yourself you'll need those magic spring compressor efforts or boing!!!!
