This week's book giveaway is in the OO, Patterns, UML and Refactoring forum. We're giving away four copies of Refactoring for Software Design Smells: Managing Technical Debt and have Girish Suryanarayana, Ganesh Samarthyam & Tushar Sharma on-line! See this thread for details.
No one can tell you how much memory your application will require, but you can use jvisualvm tool to monitor the heap memory usage by your application.
after java 1.6.13, jvisualvm is distributed with java SDK.