In theory, past papers won't be a problem.
There is a slight trap though. If you do too many past papers now, you may not be bothered to do them later come exam time. Some people will think that because they've done it before, it won't be of much use to them.
More often than not that's a misconception, but every now and then it does matter.
Past papers are a good call, but I would advise sticking with trial papers if you're going to do so. In my opinion, NESA papers are most valuable at the very end, right before you sit the final exam. This is because (despite the new syllabus, I still think) those questions will mimic the final exam better than anything.
In saying that, for practice trial papers/half yearly exams/minor school-based assessments/etc. I think that is a great idea. (Provided you're ready to tackle them of course, but presumably since you're asking this question already you may as well give it a shot regardless.)