I just completed the show, and I loved it. There are only two questions in my head. And I think there are no definitive answers to them, they can be mere speculation, but still I would like to read those. I searched a lot but couldn't find answer anywhere so I came here.
First, why was Todo so hell bound interested in creating a witch that can restore witches race? He was human and as much as it is shown, he wasn't madly in love with Maria (she was just a test subject for him, said by Father Juliano).
Second, why was Solomon so afraid of witches? Because witches were more powerful? Fine but if they despised witches so much, then why were they having conflicts with Zaizen? Zaizen wanted to eradicate witches completely, and so did Solomon. Just their means were different. And even the means could be justified because they hated witches, so creating Orbo was legal from their point of view.