Wading all depends how deep you want to go. A standard Disco can take 600mm easily so that's a deep puddle lol. I have had water coming in through the dashboard vents which is rather interesting, but I tend to keep it as low as necessary.
Extending your breathers is sensible, but then again if you're talking that then you need to to fit a snorkel because you're air inlet is at the same height as the standard breathers.
Once you have fitted the snorkel and extended the axle, gearbox, transfer box and timing cover breathers, you should then pay attention to the fuel tank breather. This is located on top of the file pipe and is the lowest vent on the vehicle.
Using 8mm dia pipe, larger than the other breather pipe, you can extend this up inside the panel behind the rear light and all the way to the roof if you want to. No it is not inside the vehicle so you will be fine.
PLEASE NOTE
Having breathers and a snorkel does not prevent water from entering the engine or the axles. They are supposed to balance the pressure differences created when a hot metal component is dunked into cold water.
Check all fluids after wading as water WILL get in through gaskets etc.
I wade as much as I can and whilst I have extended breathers to all components, the fluids can still get contaminated.
The more you wade the more you will go through wheel bearings, pads and numorous other items quicker than indicated within your service manual.
But it is soo much fun!!!!!!