If you really want to be a RAAF pilot then by all means wait a year and come back.
If you want to do some awesome flying in some awesome aircraft regardless of service, then I’d recommend considering both army and navy. You’ll have just as much (maybe more?) fun flying helos as you would flying RAAF.
As for service transfers, it happens, but if you join army or navy just to join the raaf you likely won’t last.
And as for mission, it’s not my cup of tea. If you want to be a co pilot apply for AvWO, cause romeos are awesome and hunting subs would be a hoot.
Good luck!