Howdy, Kiran!
Champion, there's no need to worry. That's why we are here, to help each other. It's likely that you'll have lots of doubts during the development, and you'll be able to find the answers to most of your questions here. If you feel that your question has not been answered after searching on older posts, please feel free to post your questions here and we'll do our best to help you!
I'd say it's harder than SCWCD, for instance. For this certification, you'll have to develop a client-server system, which involves Threads, server APIs (such as RMI), Swing, and how you divide your application, in terms of architecture. In my opinion, this is one of the best
Java certifications, along with
SCEA.
Regarding resubmission, if you are not able to get a score of 320 points, you'll have to fix the problems listed in the report (which Sun will provide you after grading your assignment) for resubmission. In this case, it will cost you another voucher.