You need to go through a pad bedding procedure to get the most out of your new pads.
http://www.zeckhausen.com/bedding_in_brakes.htm
The squeal could be caused by improper/lack of bedding and/or lack of anti-squeal compound on the backs of the pads. Also check the anti-rattle clips on the pads to see if they were reinstalled properly.
If your brake wear light came on then the sensors should have been replaced. If the light didn't come on then the old sensors can be reused. Properly installed the sensors don't touch the rotor with new pads so they shouldn't make any noise at all.