Hey nightshift! Way to go, straight for the big aperture!
You don't need to spend $2000 on a 12" - both Bintel and Andrews have the 12" GSO dobs for around $1000 or just over. You can also spend a little extra for the "premium" version, which includes a crayford focuser (vastly superior to the standard rack'n'pinion - worth the cost of the "premium" upgrade alone), a different glass in the mirror (makes no difference in australia) and a mirror fan (to aid in faster cooling down).
They come with a couple of standard plossls, but you say you have eyepieces already so that won't be a concern. Just make sure the eyepieces you have work well in a fast f/5 dob of this kind. I'm not sure what the focal ratio of your ETX is.
The difference between the $1000 and $2000 12" dobs is usually not much, or in some cases, nothing. It just depends who you buy from. I've seen some dealers advertising a rebadged GSO for 50% more than Andrews or Bintel, and they are exactly the same scope. The celestron starhopper is not a GSO, I think it's made by Synta - it has a slightly different dob mount but honestly, it is not worth that extra money. The GSO's are great quality for the price - the mirrors are just as good as Synta, and they can have all sorts of upgrades done to them if you're into DIY.
You're on the sunshine coast, if you get in touch with some of the other QLD members of the forum, you'll promptly receive an invite to their local observing sessions - there's one coming up soon,
read this thread to find out about it. There, you'll get to see some different scopes and different types of dobs, and you'll be able to make a much more informed decision.
But to be honest, you can't go past the GSO dobs (of any aperture). They have been recommended to (and bought by) many many members of this forum and not a bad word has been said about them to-date.
Bintel are a bit more expensive than Andrews for the same gear, but Bintel offer extra in the way of "service". Whether that's important to you, depends on your experience. You
will need to learn to collimate the reflector. It's extremely important - it matters not whether Bintel do it for you before they ship it, it's still something you'll need to check and fix after transportation to you, and before every few sessions as well.
Good luck and let us know how you go!