Iframes are good if you need to contain things, but if you want to access variables in those things then iframes are bad. Instead use magics and html and javascript function calls from the display library. It produces cleaner code too.
System time
Do not make programs that are dependent on system time.
Infovis
No pie charts or spaghetti plots. Avoid clutter, and volume comparisons. See the infovis section of the manual for more in depth information.
Use Python for heavy processing
JS uses the browser aka local resources. Python uses the remote Callysto Hub resources. Ideally you will do any heavy processing in Python and then pass the results to JS. Try to avoid doing large processing tasks with the user's local resources.