Can the server be set to scale the difficulty to the numbers of players registered in a world?
Playing on a public server with 100 players would affect the planet differently than a private server set to, let's say, 10 players Max; but it'd be nice to be as difficult.
So, for example, it might adjust the total number of resources, maybe representing a much smaller planet?
Yes. The world generation and game rules are in the hands of the admin. The main 'difficulty' factor is collaboration modifiers, in a 1-4 person game you will have 'very low' collaboration generally and in a high person server you'd have 'very high' collaboration. This basically limits skill rates and alters the costs of specialising in multiple fields. This is generally a better way to represent larger and smaller communities than simply giving everyone 'more stuff'.