1)
If the 200 people were called (invited), why were they l'Sumam (unaware of his intent)?
1.
Rashi citing Yerushalmi Sotah 1:8: He asked his father to write for him that the two people to whom he will show this [letter], they will go with him. He showed it to two people here, and two here
1
Radak: This is like "Mashach ba'Keshes l'Sumo" (Melachim I, 22:34) - they did not know that he is Melech Yisrael.