John and Norma,
When I made my Papa Gino's clones with the semolina, I used 15% semolina, which was somewhat an arbitrary number but within the 25% outer limit that Tom Lehmann typically recommends. However, I once had a pizza in Massachusetts where the pizza operator told me that he used about 50% semolina, but I believe that was by volume rather than by weight. In that instance, there were some leftover slices. However, they did not reheat well. The crusts upon reheating were like leather and not particularly enjoyable. I haven't priced semolina recently, but my recollection is that it was quite a bit more than the price of flour. So, that might be a factor to keep in mind.
On the matter of the hydration, when I used 15% semolina and 85% KABF, the hydration I used was around 60-61%.