I make Reinhart's focaccia a couple of times in week in about a 14 lb batch and it uses 100% preferment in the dough. I double the poolish on page 32 and use it all up. it's 64 oz h20, 36 oz bread flour, 1/2 tsp instant yeast. Minimum 3 hr ferment, then overnight it. The dough is all the poolish, 100 oz bread flour, 2 1/2 oz salt, 4 tb honey, 24 oz h20, 12 oz good olive oil,and 1 1/2 tsp instant yeast. 10 min mix, I think his focaccia formula just uses part of it. But look at the percentage. I think it's 100%. from what I can figure out, preferments are added at the rate of 20 to 100%. Maybe the thing to do to get the yeast right is to find formulas in that range and see what the percentage is. I use 1 1/2 tsp of instant for that batch of focaccia. The book is at work so I'll have to double check the percentage, but the range on that is going to be pretty low, I'd bet, maybe between .5% to 1.5%.
About the Alan Scott oven- Reinhart told me that Alan Scott's ovens are everything a brick oven can be. There are plans in one of Bernard Clayton's books and if you can find the thread here where I mentioned the beer bread, the link to Bakershelper.Com has links to a bunch of brick oven and adobe oven pages.