I'm running a D&D 4e campaign. There, a player has worked very hard and somehow tricked me into becoming a king of an evil kingdom. Good for him; he deserves it. However, how do I keep him from:

1. Going into his town's treasury and looting all the gold and buying everything in the D&D manual?
2. Rolling his army out to do quests for him?

Furthermore, how do I challenge a king intellectually and in battle? A personal army would be very annoying for me to maintain and or fight. Imagine rolling 20 times per turn.

The other players are just regular pcs and he wants to continue playing.

Any thoughts at all would be appreciated.