It definitely affects what springs you should run!
Figure on that much equipment lowering the back of the car AT LEAST 1-1.5" all by itself!
What you may find is that for the lowered stance, you ONLY change your front springs and then let "the weight do the work for you" in back and just keep stock springs.
As for the Eibachs, here is the issue. They are NOT CONSISTENT from one batch to the next in HOW MUCH DROP you get! I can show you 2 cars in ROD that have the EXACT SAME PART NUMBER spring in front, yet there is easily over 2 INCHES in ride height (one barely dropped from stock, other one is SLAMMED).
If you got yourself an Eibach set that did drop as advertised, consider yourself lucky