I did the circuit up to Jomsom about four years ago. And I did the Poon Hill loop a couple of years before. Power was not a problem - found some at least every other day. Just learn to ration your shooting in between charging opportunities. (There will probably be less on the back side.)
Take both a small Asian pin and a large pin adapter. And a light weight extension cord. Some of the outlets are funky and the small pin plugs fall out. Not a good thing when you're charging.
Lenses. Both long and short.
Obviously there are the wide vistas (learn to take panos - don't screw up like I did and keep your polarizer on).
But there are also incredible shots to be had when you won't be able to get close enough to fill the frame with a wide angle.
You might want to consider a 'monster zoom' camera such as the Panasonic FZ20 or Canon S2 IS. That would give you ~ 420 reach in 35 mm terms *and* a backup camera that would only weigh a pound or so. Might be easier than hauling a huge piece of glass.
Spend a couple of nights in a village or two. Most people just blow on through. There's a lot to see if you hang around and walk the village during the day. It's an opportunity to look back in time.
I've got some village shots on pBase
if you want a sampler.
As for batteries and temps, I was shooting with NiMH - the worst for cold. I just rotated a couple sets, warming the 'out' set under my jacket.
It probably isn't a good idea to use your portable hard drive much above 10,000 feet. If you do be very careful not to jar it while it's writing. The heads 'float' on a layer of air and as you go up the air gets thinner. You probably won't spend too much time at higher altitudes. Just treat your available card space as you would a stock of film. Be conservative enough to get back down below 10k with a frame or two left.
If you've got any specific questions feel free to send me a PM.