We currently have a problem with a lack of things for characters to do. We can assign characters to work services, but that feels somewhat pointless once players accumulate a lot of money. Furthermore, players hit the milestone by selling off excess materials very early in the game.

Could you help brainstorm some alternative ways to utilize these characters?

For example, the previous game featured a cleaning duty mechanic. Perhaps players could hire a small army of maids to make a mansion spotless and increase its prestige, or we could introduce something similar. Adding mechanics like this would significantly boost the game's replayability as a sandbox.