There is no limit to the additional sources that you use. The key
thing is that you have to at least 2 of the pieces and that your piece
includes no more than 800 words, plus the other specific requirements
listed on http://www.mixandmash.org.nz/the-competition/categories/remix/literature-remix/.
This is the criteria that will help guide judges (from
http://www.mixandmash.org.nz/the-competition/judges ) and hopefully it
will help you.
"Criteria for Creative Remix
Originality: what’s new or different about this creation?
Use of original materials: have the source materials been used in an
interesting or unexpected way?
Appeal: will people want to spend time with the entry?"
I hope this is helpful. Good luck!
Fiona
Mix and Mash NZ