Isaac,
Congratulations on your project. It's a big undertaking, but will be well worth the trouble when done.
I would suggest you look at these brands for in-wall speakers:
Boston Acoustics
Definitive Technology
In wall and in ceiling speakers fall into two basic categories: those meant for home theater use (foreground sound) and those meant for background music (sometimes called architectural sound). You'd want real home theater speakers in your 5.1 setup, but may want architectural sound speakers in other locations.
Look at Definitive and Boston for complete lines of speakers, and in particular, you need to consider what to do about subwoofers in your home theater setup. They are critically important with an in-wall system, and I always suggest at least two, for even bass coverage. Definitve makes an excellent in-wall sub product, which if you're hiding things may be your best option. All other subs are boxes on the floor, some pretty big, and almost always black and ugly.
There are many fine AVRs. I always recommend these brands: Denon and Pioneer. Onkyo offers a large feature set, but aren't generally built as well. Yamaha is also nice, but I feel the others cover the ranges most needed.
A caution on the multi-zone AVR idea: make sure you download are carefully read the manual first. Some AVRs are limited in what they can actually do for Zone 2 and 3 operation. I've gone to other solutions for distributed sound around homes.
The last thing on anyones mind is probably acoustic treatment of your HT room. In NZ, you will probably want to make your own, or have them made there. You should ask for help when you get your floor plan a bit more finalized.
Don't forget a control system. If you can't run the whole mess, it's kind of pointless.
You didn't mention picture, so let me just add that I always suggest the biggest screen possible. I've never had anyone come to me and say "Man I wish I had a smaller picture!"
