They will fit nice and flush.
If you go much lower than 30mm or so (ie as low as coilovers will go) then you might get a tiny bit of rubbing at the front.
As an example - BBS VZ wheels are 18x8 et44 (so 2mm less poke than your et42s).
I ran these with H&R springs, so a similar drop to Eibachs, and didn't have any rubbing at all.
Just a note - if you're planning to fit the springs to your standard shocks, and the shocks have a few miles on them, it won't take long for the ride quality to degrade. Shorter springs wear out old standard shocks quite quickly.
If you have the budget, either some uprated shocks like VWR or Bilstein B8 to complement the springs, or some coilovers, would be a good idea.
Hope that answers your questions :)