Possible meanings of "adversary" are 1) this refers to Satan who decided to cause trouble for Israel or 2) this refers to an enemy army that began to threaten Israel.
The Israelites considered these two cities their most southern and most northern cities. David uses these cities to refer to all of Israel. (See: [[rc://en/ta/man/translate/figs-merism]])
Joab expresses the desire for an army the size of 100 armies to say he would like the army to have more soldiers and be more powerful. (See: [[rc://en/ta/man/translate/figs-hyperbole]])
Job uses these three rhetorical questions to tell David that the census was a bad idea. It appears that David was trusting the size of his army instead of trusting Yahweh, and thus making Israel guilty of sin. These rhetorical questions can be translated as statements. AT: But my master the king, they all serve you already. My master should not request this. You will only bring guilt on the people of Israel by trusting your military power." (See: [[rc://en/ta/man/translate/figs-rquestion]])