Let the purpose drive your decision. Using IIIA soft armor may work for your application. Your size will determine your options..."normal" sized people can use the more common 10x12 inch panels which will fit in a lot of plate carriers. If you're bigger, the 11x13 panels will cover more, but may reduce your carrier choices. Vests are different cuts than plate carriers, which may further reduce your options.
If you think rifle rounds may be a threat, get some plates...which are also rated by threat protection. They may offer stand alone protection, but adding soft armor underneath may be necessary.
Steel plates are thinner, but weigh more than the thicker, lighter ceramic. Some carriers may not handle the weight of steel, or the thickness of standard ceramic plates.
My standard is IIIA soft armor for the family, and soft armor and plates for those involved in active defense. If I need to wear it for a long time or move a lot, I prefer lighter weight ceramic plates. If I'm wearing it for a short time and not moving a bunch, I'll go with steel. That being said, if all you can afford is steel, get it and save for ceramic if needed. Although in today's climate, you might be able to only get ceramic if everyone is buying the less expensive options.