Most people arrive wanting body armor and are not sure what they need. The short version: decide what you are protecting against, then buy in that order.
Handgun threats only — HG2 / Level IIIA. Common rifle rounds — RF1 / Level III+. Steel-core rifle ammunition — RF2, and this is where most realistic rifle threat actually sits. Armor-piercing — RF3 / Level IV.
Plates need a carrier. If you would rather not assemble it yourself, the kits pair them for less than buying separately.