Thumbs up for the sith costume and welcome to the 405th!
thats a pretty close deadline, i would probably say use foam for those armor pieces on the right it will be fairly quick to make and wont take nearly as much prep and finishing work as pepping I think, for the pauldron you might be able to buy that online at a fantasy armor site. the Helm would be a whole nother animal im not sure if there are any files out there for it. also take your time try not to rush if you dont make your deadline no worries just think how badass that cosplay will be with an extra year on it! also check out therpf.com theres a wealth of info on there.
i know its not much but i hope i helped out in some way. good luck and may the force be with you =)