This document outlines configuration options which aren't exposed via N1's preferences interface but may be useful.
If you want to point N1 to your self-hosted sync engine, select "Hosting your own sync engine?" under the "Get Started" button on the welcome screen. There, follow the instructions for creating your own instance of the sync engine and enter the URL and port number where you have it running.
core.workspace.interfaceZoom: If you'd like the N1 interface to be smaller or larger, this option allows you to scale the UI globally. (Default: 1)