How long can you maintain temperature without the fire?
It depends on the ambient temperature, but with a five hour fire we usually get about 5 hours in the 500-350 degree range (that's after getting to nearly 800 degrees and letting the oven drop and the heat spots even out). We start with stuff that can take more heat (like pita breads and high heat roasting) and as the temperature drops we move to things that are more heat sensitive (like baked goods with sugar in them). The oven still hangs on after the five hours. We've put a covered Dutch oven of beef ribs for braising and left it over night and it was perfectly done the next morning and the oven was still warm (but not hot anymore).
I think a key issue for this kind of baking is how thick the walls of your oven are. It been a few years ago that we settled on the Alan Scott design, but I remember looking at Mugnani ovens. If I remember correctly the home Mugnanis are really made for the "fire in" type of cooking and are made to fire fast. Does your oven have a door? You'd have to experiment with your oven, but if you have a door you could probably fire the oven for two hours or so, let the fire burn to coals, spread them across the hearth so that it's evenly heated, let them set awhile and then rake them out, mop the hearth, then close the door to equalize the heat in the oven.
For bread making to test the temperature of the oven (if you don't have a thermometer) you can throw some flour on the hearth and see how quickly it browns. If it burns right away it's too hot still. If it takes a good 15 seconds to brown it's probably okay to start baking (as long as the bread does not contain sugar). You load the oven with bread, spray some water into the oven (for oven spring) and close it up. Check it in 20 minutes (maybe earlier if the oven seems hot still) and depending on the bread you are making it will be done in 25-40 minutes. Don't be surprised if your first attempts are not so great. It takes some practice. We baked our first loaves at too high heat and the loaves sprung up to these weird ball shapes and had a crust that was hard as a rock. Now our bread is some of the best bread I have ever eaten. I know that's kind of braggy of me but we really worked hard to get it down.
I have a feeling that with a home Mugnani, you'll probably get just one cooking load, but I imagine for most normal and reasonable people that is just fine. We have a lot of pent up baking energy as we have lived without an oven in our house for 14 years.
Or we're just crazy - take your pick!
Heather