I started part 2 about three weeks ago and aim to submit before Christmas. My advice is as follows:
First, plan. Get familiar with the assignment you've been given and the deliverables that are required. Completing the assignment should take from 40-100 hours (I'm not doing the beta) depending on experience, I expect to take 50-60. Decide how you're going to split that time, put together a schedule and stick to it. Make sure as you complete each stage that you've produced all the things you planned to.
Treat it like a real project. Extract the functional and non-functional requirements from the documentation, you'll find yourself making assumptions and architectural decisions. Make notes of these and any questions as you do so. You will keep coming back to them and revising them.
Then move on and just work at it like a typical UML-based project. I've put together some system sequence diagrams and analysis sequence diagrams, they have helped me understand the interactions in the system, I am now working on packages, design sequence diagrams etc etc.
In short, produce a Software Architecture Document and you will then have much of the information you need for your submission. You then have to decide how much supplimentary information to include from the SAD and other stuff you may have done along the way.