Namaste Peter
1. surprisingly with the winter snow melt sprouts some grass for these cute Yaks to eat, when the monsoon strikes there will be tons for them to nibble on. there is live stock grazing up to 19-20,000' in summer then they go down for winter to around 10-11,000' but some places like Kyenjin have them there all year around feeding on stored fodder.
2. yep under CAN regs O2 is required by the Pilot above 10,000' but as one acclimatises the real need for it reduces, these days I am comfortable up to 17,000' without supplementary O2.
Nepalis are living as high as 19-20,000' feet all year round. We do rescues as high as 23,000'+ but we don't have the extra power to give O2 to our pax
Fly safe & happy landings
VF