Hi Matt, welcome to the forum.
It is not likely that anyone on this forum is going to answer your question. We're not intending to be mean, we just want to be safe.
Making rocket propellant and building rocket motors is not something to be approached lightly. Anyone who is really serious about learning how to do this will go to a class on the subject. Yes, there are classes on how to mix propellants and build motors. (At least, there are here in the USA)
Perhaps someone here on the forum can direct you to sources of classes in New Zealand.
- Ken