You don't want to to do a true bed until the pads are fully and evenly contacting the rotors or you risk pad hotspotting, and even smearing the rotors. There's no downside to waiting, but there is for doing it too hard, too soon.
As for noise, yes slotted rotors will hum, and will buzz when you brake harder but I personally like that sound and feeling. Also, I chose slotting specifically for its ability to automatically deglaze the pads, and to promote more even- albeit accelerated- pad wear. I don't like loud squeal but that's unrelated to slotting- blanks will do it too if you select the wrong compound or do a poor installation (i.e. not using the right pad lubricant, or not cleaning the contact areas of the calipers before installing the new pads).