My Few Cents :
As the instruction in the assignment says, you will need to use Java/JEE components in design. So best choice for business tier would be EJBs and for intergration tier would be DAOs specifically for communication to external systems.
For DB, its at your own discretion/ design choice.
Your architecture should be N-Tier based clearly calling out the JEE components being used in the individual tiers, using design
patterns as best/standard practices. As far as possible, try to follow n-tier architecture in all diagrams including class,component,deployment and sequence.
In addition to the above, I have provided notes for all diagrams and extensive explanation on sequence diagrams depicting detailed technical flow for each use case, ie. one sequence diagram per use case ( as per cade and humphery sheil suggestion in chapter 9 of their book )
Hope this helps!!!