Prius Gen 2 Double Din Upgrade

I have a 2006 Prius i-Tech (Australia - RHD model) and it's time for a stereo upgrade.

I have read numerous articles on how to do it and what my options might be, but I have a few questions that I can't seem to find answers to. I'm hoping someone here might be able to point me in the right direction.

1 - I need a Double Din adapter to plug up the gaps either side of the stereo. There are various models available, but although they say "Double Din", they typically AREN'T "Double Din". Double Din is supposed to be 178x100mm, which is the size of the stereo that I have (a Joying Android 7" touch screen unit). The adapters that I'm finding all seem to be a little smaller and result in having to dremel out the gap or jam the stereo in anyway, resulting in the adapter bulging, twisting and looking generally dreadful. Can you actually get a true double din adapter? What do people do? The articles I've seen show people with double din units installed using what appears to be a common adapter, but they don't say if they had to modify it or not.

2 - Some of the double din adapters come with a mounting bracket and some don't. I'm assuming that the ones that don't expect that you'll reuse the original one. But if you can do that, why would any of the adapters need to come with their own bracket? Some seem to come with an optional bracket - which again seems pointless if you can use it without said bracket.

3 - As my car is a RHD model, will any adapter fit? Or do I need one specifically for RHD? None of the adapters I've seen mention RHD or LHD so I'm assuming they're the same, but I don't want to buy one, only to find it's the wrong shape for my dash. And if the LHD ones don't fit, where do I get a RHD one?

4 - It seems that the JBL amplifier does half the work of the stereo, such as volume, equalisation, on-screen display, speaker crossover etc, so either I need an adapter to allow a standard stereo to work with the JBL amp, or I bypass the JBL amp altogether which sounds like way too much work. How good is the JBL amp? It sounds quite good in the car, but I wonder how the amp that's built into my head unit would compare and would it be worth adding crossovers to my speakers and just using the new stereo without the JBL amp.

Thank you all for any assistance that you may be able to provide.

Chris