A good way to build an first app in Python would be to go through the google app engine docs for python, they provide the ability to deploy your app and have a good api. To learn javascript, if you already know C the syntax itself is a lot like C, but there is the dom and dynamically typed variables. A good way to start might be learning some javascript basics and taking a look at jQuery: http://docs.jquery.com/Tutorials:Getting_Started_with_jQuery. Hope that helps!

Are there any specific libraries or features that would be particularly salient to this endeavor?

for javascript in the browser jQuery is a godsend.

if you like functional programming check out underscore.js

jquery ui is a jQuery plugin that eases many ui tasks, but be careful - it's easy to go overboard.