Andrew, I've actually been thinking about this since you asked about hearth materials a couple days back. A gas oven with a broiler below is, honestly, just about the worst configuration you can work with.
Up until now, for these kind of separate broiler configurations, I've been recommending two stone setups in the main oven compartment, using quarry tiles for a ceiling and then filling in the rest of the shelf with foil (to isolate the thermostat), and the results seem to have been pretty positive, but... now that I think about it, covering up an entire shelf with tiles and foil could block air flow and in a gas oven, that's not a good idea.
I've never seen a traditional NY style pizza done well with the skillet method. Heston Blumenthal and his assistant Chris Young, who, from what I understand pioneered the skillet method, have produced some atrocious looking pizzas. Kenji's taken it a step further, but it's still not what it could be. I believe John Wozniak (johnnydoubleu) uses a skillet technique (along with a separate gas oven broiling compartment), and if anyone can master the technique, it's him, but he leans towards non traditional pizza. I haven't tested this yet, but I believe that pizza needs heat from all sides in order to achieve the best possible oven spring. The intensity of the heat might be up for debate, but I think that starting a pizza in a skillet (with no top heat) and then broiling is not ideal. A typical cast iron skillet is 1/8", so you can't pre-heat it and then expect it to store enough heat to bake a fast pizza. I guess if it was close to red hot, that might produce a fast bake on the bottom, but... it would be a lot of heat at the beginning, with much less heat at the end, and I'm not sure that could produce typical NY style undercrust browning.
I've known some folks that have pre-heated stones in the main compartment and moved them to the broiling compartment to bake the pizza. This makes me incredibly nervous.
All that's left is putting the stone in the broiling compartment and using the broiler to pre-heat the stone. I've talked about this before, but I feel that broiler pre-heats tend to be a bit superficial. They give you a really hot surface, but the core temp of the hearth doesn't get as high as it should and pizza is baked with stored/core temp, not surface temp. The other down side is that broiling compartments can be small, and, for NY, bigger is always better. On the plus side, you don't need any gaps for air in the bottom of the broiling compartment, so you can size the stone to fill the shelf.
Assuming you could fully penetrate the hearth with heat with the broiler, I think it would take a long time- much longer than a bake pre-heat. If you could position the hearth close enough to the broiler, perhaps you could trim that time (and maybe help with core temp), but you've got to fit a pizza in there. You know how some charcoal grills have a lever that raises and lowers the charcoal shelf? I've always dreamed of being able to lever the hearth so that it's almost touching the broiler during the pre-heat, and then lowering the hearth for the bake.
Until such a contraption exists... I would see what you can do with a 1/2" thick steel plate and a broiler pre-heat. Size the plate so that it fills the broiler shelf and raise it as high as you can while still fitting a pizza between the broiler and the plate. Put the broiler on for an hour, watch it and see if the broiler cuts in and out, then take temps of the top of the plate AND the bottom the plate (with a $20 IR thermometer, if you don't have one).
What are the dimensions of your broiler compartment? Please tell me that you can fit at least a 14" square plate in there. For NY style, 12" pizzas kind of suck.
You want a36 hot rolled (aka 'mild') steel plate. Don't buy it online, but here's a reference:http://www.onlinemetals.com/merchant.cfm?step=4&pid=9610&id=839&top_cat=849
Re; the scale. I don't think there are any particular brands that are more reliable than others, it's a matter of features- such as increments, total capacity and a pull out display. Here are my most recent recommendations:http://www.pizzamaking.com/forum/index.php/topic,8093.msg108415.html#msg108415
A pull out display or an elevated platform is really nice so you can read the scale with big bowls on it, but... I've lived for 15 years without them. If you're short on funds, just get the Walmart scale. At the end of the day, it's WAY more important to have a digital scale and use it then to wait and find the 'perfect scale' or to take a while to save up for just the right one. Just make sure whatever scale you get goes up to at least 5 lb (and preferably 11) and does so in 1g increments.