Norm and I lowered our cars by installing the 1 Bump rear pads (Had 2 Bump) and we did before and after measurements. We haven't had a chance to do the fronts yet since we didn't have the right tool but we will be doing this shortly.
Yes you will notice a difference but not a significant one.
Right now my cars rear is lower than the front and it looks / feels funny.
The rear is a DIY and you will need a socket wrench, jack and stands. An extra hand would also be helpful but thats all. Should take about 40 minutes to do yourself
The fronts require a special spring compressor (expensive!) and are more time consuming.
A 2.5 Hour quote from the dealer is about right, any more would be too much.
Just a note on alignment. Normally the 124's have a slilghtly negative rear camber, after lowering this will be even further negative. The bad news is that rear camber is not adjustable unless you buy an aftermarket kit
so your tire wear will increase on the inside of the tire. On the positive side handling and stability will improve.