I have a Hitachi HB-D102 that's about 20 years old. It bakes a vertical loaf so I rarely use it and when I do, it's only to mix the dough. The recipes that came with the machine all use 3 cups of flour.

I have a recipe for challah that calls for 6 - 6 1/2 cups of flour and 3 eggs. "Makes 2 large challot, about 1 2/3 pounds each." First of all, I'd like to know how much flour can this machine likely mix without burning out the motor. Hitachi no longer offers support for this line so I Googled "HB-D102 motor" and found that it is supposedly 90W.

But this recipe is really larger than I need. Since it calls for 3 eggs, is it appropriate to multiply ALL solid and liquid ingredients including yeast by 2/3? In other words, except for eggs, do baking recipes scale linearly?