How about using one of the digital voltmeters that comes with a built in serial port for logging ?

That should work - i guess

Might cost a little too much

You need to figur out how much current (and at what voltages) each unit/device needs when running. This is not trivial :-)
Then you need to figure out how long tim your setup should be able to run powered from the battery.

Then you can start calculating what battery you need.

You also need to take the total max power dissipation of the Nano into consideration, is it even possible to run all those things of the Nanos voltage regulator ? (i doubt it).

Check this site:

http://www.stumbleupon.com/su/1ZsVg5/genericnerd.blogspot.com/2009/05/arduino-mood-light-controller.html/

If you just want to control the RGB levels, you can skip most of the components in the lower left part of the schematic.

It's about 1000 RGB LEDS or the equvivalent of 3000 individual LEDs (20 cm apart = 25 pr/m2).

But that is still a very large amount of LED's to control individually.

I would do as GoForSmoke suggests, create a modular design with a local controller for say each squaremeter controlling 25 (75) LED's, then hook up all the local controllers somehow to a "central intelligence unit".

There are lots of potential trouble spots, including power supply and method of controlling 40 individual modules.

I think we need a little more information

It would help a lot if you told us:

    -what senor it is
    -where the datasheet for it can be found
    -how you hooked it up to your Arduino

And maybe posted your code.

I don't know what drivers come with the Leonardo board, but the ordinary Arduino board uses drivers for the FTDI chip.

Try to find out which drivers the Leonardo board uses and reinstall them.

No there is not really anything you can do, except by an Arduino Mega that has more flash and more RAM.

Of course thee is always the possibility that your sketch can be optimized / rewritten in some way to take up less space.

First thing i would check is the Java version and upgrade if needed.

The problem has been fixed in GoBetwino

http://blog.makezine.com/2008/08/13/laser-modem-with-an-ardui/

Does it have to be Arduino alone ?

Could you use Arduino to read the flex sensors and offload the gesture recognition to a PC ?
That would be much better.

the most important thing is to choose an Arduino board that matches the WIFI board you choose.

I think logging to an SD card will be much easier.

WIFI is going to be difficult for such a large area, and it will use more power.

How are you going to monitor temperature? on the surface of the sheep? Direct unlight could be a problem.

How small is "a small area"?
How large is the animal ?

How many hours will you need to track the animal?

Battery power will be a potential problem, especially if you go the wifi way.

Is it possible that you are using up all the available RAM ?