Franny, this oven, with the right stone, can make a NY style pie that will massacre Bobby G's, Caputo on the grill and the 2 old stone Wolf pies. Having it around just to 'warm up Sicilian,' is heresy, imo
It's like owning a Ferrari, but leaving it in the garage. As far as deck ovens go, I think these are somewhat cheaply made, but any oven that can bake a 16" pizza at 650 deg is worth it's weight in gold. Your Wolf can't hit 650, and, while the grill most likely can, I highly doubt it can handle a 16" pie.
It's your oven, so you can do with it as you please- I'm just telling you that you have a piece of equipment there that can do majestic things with, if you approach it the right way.
Fire brick, from what I understand, only comes in 2.25 inch bricks and 1.125 inch 'splits.' I'm not sure splits would be right for this oven. Splits will take way too long to preheat and their weight will most likely stress those shelf supports. If you really do want to just 'play' with this oven, then go with the 3/4" kiln shelves- I would suggest that you find a ceramic supplier near you, so you don't have to pay exorbitant shipping. Axner's stone is $30, but I think the shipping comes to $20 more. Bear in mind, the 3/4" stone will give you completely different results than the existing 1/2" stone, so, if you do ever start using this oven for real entertaining, I don't think you'll be able to bake multiple pies at the same time using the two different stones.