Yep I agree - completely doable.
I completed all of my exams using what are now the Waypoints series and Ross Ewing's book for human factors.
If you're worried about the currency of the content - the syllabus is available in Advisory Circular 61-3, APPENDIX II:
http://www.caa.govt.nz/assets/legacy...rs/AC061_3.pdf
That should indicate everything you need to know for each subject. Sounds tedious but works a treat.
Then all you have to do is sign up with Aviation Services Limited (ASL)/ASPEQ and book/sit exams as you see fit:
caanz.aspeqexams.com/
Good luck!