Current questions and answers regarding the map editor.

1) How can I add more Red Knights to the scenario hero panel? I mean, besides Benedict, Gabriel, and Valeria, can I also add, for example, Andreas and Lorenzo?

I don't quite understand the question. You can select any hero, press the spacebar, and choose Andreas from the list. Or is he not in the list? Then, go to the left panel of properties, click on the ellipsis to the right of Shared, and select the desired hero from the newly opened list.

Or should I enter their number and name in the empty space?

Exactly. Even if it freezes there, just enter it, and that's it.