Frankly, I just saved up and bought Lvl IV stand-alone ceramic plates from SKD when they had a group buy.
I suggest that you do similar. There are very important reasons why steel plates are not bought by the Mil or police.
When the price of anti-spall backers is included into the purchase price of steel plates, the price difference shrinks dramatically.
Assuming you want the heavier steel plates, and the additional weight of anti-spall backers, just where does the impacting round go? With ceramic plates, the bullet's energy is absorbed within the plate., and damages that particular portion of the ceramic plate.
With steel plates, and assuming no potentially injurious spall (damage to the steel plate) from the back of the plate, the bullet ricochets somewhere and with some velocity. Might be your arms, legs, or throat.
Again, the Mil and cops don't buy steel plates, and there are good reasons for their not doing so.