Thanks @zenofmud and @drmibell for the practical tips. Most useful.
Out of interest @drmibell, re your earlier post where you suggested a JSON file. That's what I originally envisaged. Sorry if this is a basic question, but would you literally create the file with a text editor to start with? If you wanted to update it programmatically (e.g. one item might be a stored lighting scene, and there may be an option on a control panel to overwrite an existing scene with new settings) - I'm guessing there's a good way to do that?
Or do we get into possible problems with concurrency? Perhaps it may be better to store all of the json in persistent storage? Hopefully I didn't misunderstand your point about using JSON file for static information about devices and a global variable for state information...
