1)
What is the meaning of "va'Ydaber Yehonason b'David Tov El Sha'ul"?
1.
Targum Yonasan: He spoke good things about David in front of Sha'ul.
2.
Malbim: He spoke bad (refer to 19:3:3:1 and the note there) about David, e.g. he risks his life too freely, and Sha'ul was happy to hear this. 1 He then said, even though David himself sins, all his actions are good for you - you should not harm him.
1
If so, it should say v'Hayah Tov El (or even better, b'Aznei) Sha'ul! Also, he should have 'but' or 'even so' before saying why he should not harm him! (PF)
