(i) you have enough time !!
(ii) AIMR policy: no refunds
(iii) you can defer, but as pigmy implied, you would need to pay the exam fee again, barring something like SARS occuring again.
The only advantage in deferring rather than just not showing up is you don't need for the results to come out before registering again.
look over the AIMR website. There's usually a deferral form on there (use the search tool if you need to)