Hi,
I notice you are in Mount Beauty therefore I would say you dont need any visual filters at all. Your skies are wonderfully dark and you also have some elevation, you lucky bu%&*er
From your equipment list you appear to have no mono cameras so i dont think you need a set of RGB filters.
For just starting out i am basically saying you dont need any filters given your location except for a UV/IR cut filter for imaging. This will remove a bit of bloat from stars and is not really necessary but people do use them. As you progress you should consider a narrowband Ha filter. This will allow you to image even during a full moon and you can add this data to the data you get from all your one shot colour cameras.
Having mastered Ha, you may like to add an OIII and SII and try some narrowband imaging.
As far as brands are concerned I always buy Astronomic gear as I find the quality and robustness worth the price.
Basically though stick with your D80 and see how you go
, obviously if you have the money an EOS 40D or QHY8 would be a far better addition given your location than multiple filters.
Cheers
Paul