Ron, two things.
First, you really need an IR thermometer. You can get one for as little as $20 shipped.
Secondly, my previous comments were based upon the premise that you'll eventually want to be baking a relatively fast NY style pizza. If you're okay with other slower styles, you have a little more flexibility. I don't think other styles will give you the kind of flexibility to work with steel, though. Steel in a bottom heat scenario is a recipe for a lot of headaches. I would say that the go to stone for people that want to do longer baked pizzas on a grill is cordierite. It's very durable, it has good conductivity (but not too high) and holds stable temps. Out of all the options, though, cordierite baking stones (Bed Bath & Beyond, Williams Sonoma, Pottery suppliers) are usually the most expensive. Quarry tiles can have issues with direct flame, but, if you put the tiles on top of the steel plate, you should be okay.
Either cordierite or quarry on steel should make your life a lot easier. Neither will give you a fast NY bake, but if that's not what you're into, then those materials will work just fine.