I doubt the soap and water makes all that much dif. It's just to remove any residue that may have been applied to the rotors to inhibit rust while sitting in a warehouse somewhere. I'm sure a lot of people don't bother with that.
If these are OEM pads, it is not unusual that squeek at low speed braking. I' used to hear that all the time. It's just the pad chattering from light contact with the rotor. You noticed those pads are a bit floppy in there, didn't you? They're designed to slide easily over the pins and in the calipers. The caliper piston moves in and out perfectly straight and smooth because it is hydraulic but the pads just hang in position loosely.
I think my OEM pads and rotors got less squeaky with some use but I remember it would crop up now and then. I have been happy with the combination of OEM rotors and EBC HHH scintered pads. They were nice and quiet all the time. I started to get a higher speed groan once in while with that combination which is more disconcerting.
08 MIDNIGHT SAPPHIRE BLUE ZX-14 Now Deceased, will be resurected
2024 ZX-14R bran friggin NEW!