1. Yes, the price you see on Amazon is the full price of the book; the only extra you will have to pay are any applicable taxes, such as GST or VAT. However, many of the non-free books have the Whispernet surcharge included in the price, so you will often see books in the Australian Kindle store appear to cost $2 more than the same title in the US Kindle store.
2. You can have both credit cards and gift card balances in your account. You'll have to set one as the default 1-click payment method, but you can switch between both.
Possibly the best way for both you and your dad to use your Kindle, but keep your purchases separate, is for your dad to buy Kindle books on his own account, and you to buy them on yours. Amazon lets you share books between family and friends' accounts, so if there's a particular title both you and your dad want to read, you don't have to buy it more than once; only change the Kindle device registration and re-download the books as appropriate.
You can de-register and re-register the Kindle to each account in turn to switch between them; the books are all DRM-coded for a particular device serial number, not for a particular account, so you can have books that were bought under your dad's account still work on your Kindle even when it is currently registered to your account, and vice versa.
In the meantime, you and your dad can download the free Kindle for PC/Mac applications and register them to your respective accounts so that you can each keep buying books, regardless of whose account your physical Kindle is attached to, and also be able to read your purchased books on your computer, as well.
3. Buying not-available books in other countries has been discussed a lot in these forums, and there are plenty of threads. Basically, the way to do it is to register a US (or other country) shipping address and pay using gift cards. If you go this route, please be aware that if Amazon catches on, they will ask you to provide proof of residence in the country you've chosen.
For best results, I'd advise making an entirely separate account for this, and only ever using the "Download via Computer" option when buying the books, rather than letting Amazon send the new purchases direct to your Kindle via Whispernet. You may also want to look into using a US-based VPN or proxy service to mask your Australian IP when you buy and download from the US Kindle store. There are free ones which you can find discussions on elsewhere on the MR forums.
There are a number of package re-shipping services in the US which specialize in providing non-US customers with a mailing address so they can buy stuff and get the cheap/free shipping often available within the US, before sending it on to their home countries for a lower cost than international shipping usually costs in most stores.
4. Yes, if your credit card company charges foreign currency conversion to begin with (Amazon itself does not tack on any extra fees).
That's why a lot of non-US customers like to use the gift cards. Tiny little charges can add up, especially if they're rounded up; also, CC companies don't like lots of small charges under $5 or so. If there are lot in a short period of time, that can sometimes trigger a fraud-protection plan and block your CC until one of their representatives calls you up to confirm that it was really you spending that money.
If you buy a reasonably large denomination gift card, you can avoid both of these situations, and if you buy the GC when the exchange rate is favourable, then it can be a better deal than separate CC charges over time as your currency fluctuates up and down.
Finally, there are many other places outside of Amazon where you can get Kindle-compatible books, both free and pay. Project Gutenberg Australia, especially, has many famous classic books that are free to Australians which have not yet entered the public domain elsewhere, such as Margaret Mitchell's Gone with the Wind, among others.
The format you want to look for is DRM-free Mobipocket. It comes with the filename extensions .prc, .mobi, and .azw. You can also download just about any other DRM-free format and convert it to Mobipocket using the free application Calibre.
Avoid "Secured" formats, they will not work on the Kindle, and you cannot convert them without breaking the DRM, which may or may not be legal in your country (e.g. it's legal in Norway for personal purchases).
Hope this gives you everything you need to know. If you've any more questions, please don't hesitate to ask.
Last edited by ATDrake; 05-31-2010 at 04:38 PM.
Reason: Correct typo, add extra info.