Map size

World sizes above 2.56 km² aren't supported by us, such over 4km² have never been. You can still try to change the WorldGenerator.eco respectively, but the outcome depends heavily on your and users hardware resoruces. The setting in the client to change world size is purposefully limited to the maximum supported size.

Yes, you would need to start the server manually by starting EcoServer.exe if you want to use your own configuration.

Yes, the single player simply starts a local server through the client.

To start it in a dedicated way, via the EcoServer.exe, you'd need an SLG account that owns eco. You can create one for free and link your Steam account to it, granting the SLG account the game for free.