According to the yerushalmi
the King also has to ask a navi before going to war .
According to Ri Migash 21b The Monarchy is entitled to have funding for intelligence,deception,espionage
As for Lo Yarbeh of treasure
Rambam forbids a king to even keep money and possesions which came to him via conquest
The Ramah and Ran however permit .it is only forbidden to levy excessive taxes