One thing I've been reminded of when reading through this thread is the need for an 'Exit Strategy', that is how, when, and in what circumstances do you intend to dispose of your stack?
If you've bought numis/semi-numis at less than $500 (each or as a set) as a collector, and sell them at less than $500, then they should be exempt for CGT purposes. If you've bought bars and rounds, they are probably not considered as collectables by the ATO, and may be liable for CGT (and the CGT discount if held for more than a year - for which you should keep records).
For the OP - you might consider getting advice from a tax agent/accountant relevant to your personal circumstances.