1)
Why was Yonason not with Adoniyahu from the beginning?
1.
Malbim: He remained in the city to spy what will happen when they gather outside the city to make Adoniyahu king.
2)
What is the meaning of "Ish Chayil Atah"?
1.
Radak: You are zealous and good.
2.
Radak citing Targum Yonasan: You fear sin. I.e. you have strength to suppress your Yetzer [ha'Ra].
3)
Why does being an Ish Chayil imply that he has good tidings?
1.
Malbim: Presumably, he gathered Giborim of the king and blew the Shofar amidst rejoicing over Adoniyahu's kingship.