Unless your development organization is stuck using
Java 1.4,
you should move to JUnit 4 which does not require you to extend TestCase.
In answer to your questions:
1. setup() is used to initialize test fixtures and preconditions that are common to all tests. If the cust object is going be common to all tests, then what you did is fine.
2. assertEquals() can be used with pretty much anything, including Strings.
3. Yes, you can add more test methods.
For effective use of unit tests, I recommend you read up on the practice of Test-Driven Development.
For me, unit tests will become part of the detailed design specification, providing concrete examples of how you should expect classes to behave under different conditions. Unit tests should be FIRST - Fast, Independent, Repeatable, Self-verifying, and Timely. Unit tests should help you drive design thinking, help you make better design decisions, as well help you refactor your designs safely. Understanding these things before you move on down the path you're heading now will hopefully make you rethink your approach to using and writing unit tests.