Diplomatic is Indonesia's best bet. You can rake in more gold from the unique luxury resources, and it forces you to trade them and keep friendly nature with other civs. Remember, the resources have a +2 base, in addition to the gold you get from trading your extra copies. Also, being friendly fosters trade routes which fosters bringing in foreign religions from those routes - which can give your candi +10
Domination is also viable. Remember, if you conquer a city on a foreign land before actually settling on a different continent then you get the unique luxury resource. If you get favorable Kris Swordsman upgrades, that is something to consider if you don't mind dealing with the repercussions.
Definitely. Going for a kill across the sea can be a huge boon, letting you snap up both a new city and some new lux resources to help fight the gold and happiness costs of maintaining a war.
Plus, Kris promotions are maintained throughout the upgrade cycle, meaning that a Kris swordsman with a good promotion can easily become a Longswordsman with a good promotion, and so on.
Crazy question... if I build a Kris Swordsman and gift it to Japan, will he upgrade it to a Samurai when Steel rolls around? Could you have Kris-wielding samurai?