1. They are Tzimisce modified ghouls for warfare (monstruous beasts). They can be spawned as Men at Arms with a character interaction.
2 and 3. It's not yet implemented.
4. You guessed correctly.
5. Fame is way easier to come by in the mod (you might have seen some clans, like the Ventrue and Gangrel, starting with high level of renown). In order to get the player to play to 1500 (our endgame), the progression is slower than vanilla in most things (lifestyles, these kind of CBs etc).
6. As a one off? Not really. But you can combine several of those with some house modifiers and have some quite impressive Men at Arms. They shine mostly during the endgame, where your knights can be overwhelmed by the sheer number of Inquisition troops without some support.
The game ends in 1500? That's odd. I actually peeked into the game files recently to see what great persons are available, and noticed that you, for instance, have Elizabeth Bathory spawning at 1614, though.