customize My java google app engine application

I have a Java google app engine Application I'll like to customize with additional features. the application [login to view URL] helps users schedule their tweets with a text file or directly from the admin section and I'll like to tweak the feed subscription option + improve the user interface in the admin section (javascript/jquery), implement my new landing page on the landing page and give me an overview of all users and their activities in the admin panel + implement openID as login option or signup with email and password. Implement a payment processing with paypal. That's pretty much it, feel free to ask any additional question. The app is written in Java and run on Google App engine, but if you'll rather prefer to rewrite the app from the scratch with python, I don't mind.