Hi, we only use nuc sized units for queen rearing now. We do it differently to your plan but it's the principle that matters in this instance rather than the methodology. I just find it preferable to use a handful of nucs which can be actively cell raising or resting, depending on what's needed rather than one or two big units. Personal choice.

I'd personally not worry about getting the maximum take although a powerful nuc will do your twenty +/-. Looking at it from the mating end of the plan I'd aim to have maybe three or four batches of ten or so queens going through (having made maybe 14 grafts to begin); more potential drone diversity and plenty of wriggle room for getting out of problems with the weather and other general mishaps.

Several small batches also give you a built in opportunity for culling some, this is something I now believe to be even more important than selecting the mother.

A final advantage is that you'll be extending your practical experience of hands on queen rearing through the season, that's important because with our relatively short seasons it's hard to get hours on the clock.