Eibach Prokits never go low enough, you'll want to go Sportlines, trust me.

Pretty much any spring will work with stock shocks, but the lower you go, the more likely you will blow them.

There's no definite period on when they will go, but aftermarket shocks are a worthy investment. Not only will they make the car handle better, but the ride quality will be less bouncy from the get-go.

I personally recommend Sportlines (~1.8 drop) with KYB AGX or GR2 shocks.

You're also going to want to look into getting an alignment once you're dropped.