Which Arduino to buy, and what to power it with?

I'm working on a project that has a 3x3 grid of 8x8 LED arrays, on which graphics will be printed. Which Arduino would be the best one to use? I'd also like to have some audio processing, and the whole thing will hopefully be controlled by some pushbuttons and an android phone.

I'm also having trouble figuring out what to use for a power supply. The project will be installed on a portable/wearable structure, and I won't have access to 110/220 outlets. Any help would be greatly appreciated.

That are many questions, and each problem has a number of solutions. Perhaps you might need to drop some features, to be able to finish the project.

Arduino : It is best to start with Arduino Uno. That is the most common Arduino Board. http://www.arduino.cc/en/Main/arduinoBoardUno

If you get to know the Arduino Uno, you can decide where to go next.

Using a mosfet or transistor to switch leds is not hard. Using a battery (for example a Li-ion battery), perhaps with a DC-DC converter is possible. Audio processing with the Arduino Uno is possible with some Audio/Sound/Voice shield. Wifi is also possible with the Arduino Uno, with a Wifi Shield. http://arduino.cc/en/Main/ArduinoWiFiShield

But an Arduino Uno with a Wifi shield and a Voice shield and output stages makes it complicated. I don't know the XBee boards, but perhaps such a board with wifi is a better choice. I think it is Arduino compatible.

I'm also having trouble figuring out what to use for a power supply.

Is a car battery an option, with a proper voltage regulator you can run an Arduino + extra for quite some time.

I'm working on a project (first time working with both LEDs and Arduino) which involves a 24x24 array of LEDs. The array is made up of a 3x3 grid of 8x8 LEDs, each driven by a MAX7219. The array is being installed in a wearable helmet, and needs to be portable. It also needs to be able to last for at least 2-4 hours on a single charge, ideally more. Will something like this rechargeable battery shield do the trick? http://www.liquidware.com/shop/show/BPM/Mega+Backpack

Also, as this is the first time I'm attempting to work with these materials, I'm really not sure which Arduino to buy. The final product should be able to display different animations (no more than ~300 individual frames). I'd also like to have an audio input that can select different frames to display based on input volume levels.

Any guidance on this project would be very appreciated. The Arduino platform seems to have limitless potential, and I can't wait to see this whole thing completed.

A car battery wouldn't work, as the power supply has to be either inside the helmet itself, or in a backpack. I'd rather not carry 50+ pounds on my back for several hours :D

Have you measured the average current consumption? Why not?

I merged these two because I thought they looked so similar.

I have not measured it because it's still in the planning stage, nothing is assembled. I'm trying to get input from people who know more than I do before I buy a bunch of things that won't actually work for my project. I don't know much about the arduino and its capabilities, so I'm not sure how much power I'd even need to make the thing run, or even how many LEDs would be lit at the same time without visible flickering.