The Shellback Tactical Shield Active Shooter Kit plate carrier does not have the ability to insert side plates into the cummerbund. It will only accept front at rear 10x12 plates.
The NIJ level IV threat protection plates are rated for 357 SIG FMJ, 9MM, .38, .40 S&W, .44, .45, .223 BALL, 5.56X45 (XM 193), 7.62 X 39 BALL, 7.62 x 51 M80 Nato, M855/SS109, 7.62x54R API, and 7.62x63 M2AP.
These plates are level 4.
30.06 M2AP 166gr (armour piercing) travelling between a speed of 2850fps and 2900fps.
The weight of each plate will be 8.2 lbs. Unfortunately, the weight of the carrier itself isn't given, but the total weight should be around 20 lbs.