It's hard to tell without ingredients, quantities, and details of how they're being handled. But we'll assume a valid recipe and proper technique and make a few points, because I suspect that you might be trying too hard to do things "French."
Steam is kind of hard to do in conventional ovens, and all conventional ovens differ. I'd suggest instead to brush the dough with water just before they go into the oven. I used to spray or poor a cup of water into a hot pan in the bottom, but it was no better than brushing.
When using stones or bricks, it takes a while for them to come up to temperature all the way through, so that they can do what you want them to do. Preheat with them in the oven for 30 minutes or longer on very high heat. But you really can't emulate a brick oven without, well, a brick oven. What you can do is build a brick oven within your oven. A stone floor, side uprights, and a stone cap, so the bread goes inside. WAY too much fooling around for the marginal difference it makes. I've tried stones, but I make mostly baguettes, and nothing beats my perforated baguette pan.
Now, you said you took measurements before having the stone cut. Does that mean you lined it all the way side to side and front to back? That will defeat the oven's function. The heat source is at the bottom, and much depends on the flow of air up around the bread. That may well be the source of the crust problem. It may just not be recovering from having the door open, and that first few minutes is critical to the crust. Try just one stone or just enough for the loaf, in the center of the rack. I'm very leery of anything bigger than absolutely necessary. A lot of testing and engineering went into designing the oven to correctly maintain and distribute heat. Remember how a wood-fired brick oven works. The wood is fired and the oven heated and the wood pushed to the sides and back. The heat is from all directions.
I don't worry about the classic crumb with big holes. If I get it, fine, If I don't fine. But I find I get better results if I let the dough rest for a 20 - 30 minute period to autolyze before kneading. There's a very distinct difference in the texture of the dough and a better crumb.
Recipes for, say, baguettes, are pretty generic. But this is close to my basic, and I've never had a failure. I have to say that I adjust by sight and feel to compensate for changes in humidity by bumping the flour while kneading in the mixer, having the dough just hard enough to clean the sides of the bowl. And I take some care in working the dough into baguettes. (But don't take the specification for "bread flour" too seriously. American all-purpose flour is pretty close to what they use for bread in France. I find little difference, mainly bolder crumb with bread flour. Meh!
Classic Baguettes and Stuffed Baguettes: King Arthur Flour
And see the blog photos:
Baguettes: DO try this at home. | King Arthur Flour
I would, at his point drop back, take the stones out, and just execute the above on a parchment lined baking sheet, to guarantee a success, and then move on changing one thing at a time, if you want to try the other stuff.
