Dropbox list: there are a few workflows in the directory that'll probably help you here, but as a starter, you can use something like:
p = editor.get_path() print(p)...with a Dropbox file open in the editor to get the path.
UI module: I copied the stopwatch example from Pythonista into Editorial, no problems.
Installing modules: possible to an extent, but not as convenient as in Pythonista. See here: https://forum.omz-software.com/topic/3921/library-module-for-editorial-via-pythonista