If, by normal home use, you mean surfing the web, checking email, playing the occasional game, etc, then I would think you might be better served by getting a new iPad instead of an older or used Mac laptop. iPads start at $500, which would leave you some cash to accessorize and buy apps.
As for buying from Amazon: I've been buying from the United States version of Amazon for many years and have had very few problems -- and of the few problems I did have, all were immediately and satisfactorily resolved by Amazon. I have no idea whether Amazon's Australian branch is as reliable, but I would imagine that to be the case.
If you did opt to buy a Mac laptop (called a "Macbook"), then, yes, you could install some Windows programs BUT there's a caveat: you would also have to install Windows -- either in a dual book configuration (you choose, when you turn on the Mac, if you want to use OSX or Windows) or inside of a virtual machine (from inside OSX you "turn on" Windows like any other program, and use it like a little computer inside your computer). Either way you'd be increasing your cost, though, as you'd need to buy your Mac AND a license for Windows (and maybe the the VM software).
If you opt to go with an iPad, as I recommend, you won't be able to load Windows programs -- but you could use something like
LogMeIn to control your existing PC (which may meet your needs).
Good luck!