What do you think the biggest technical challenge is in the project?
With the limited knowledge I have, I would say that writing a program that ensures collaborative editing, represents by itself a great challenge since I have few ideas about how to resolve this problem.
Other challenges
Work on a real project with all the parts that must fit together and so, be able to keep the whole system understandable and manageable.
Related to the previous statement: learning how to design a piece of software.
Be able to sustain a long effort even during phases where enthusiasm will fade away.