Ooops been away for a while.... Went in 2000 and 2001 no summit! Boo.. weather one year, and flu the next..
A week at 17500 was enough for me!

As to oxygen. none needed. Yep needed for pilots etc. because of quick change in pressure.
with proper acclimatization, it is OK...
we take soemtimes upwards of 2 weeks to really make it to the high mountain so your body can get used to the lower pressure..
That's why a climb on Everest can take 3 or 4 months!!

Cheers
Curtis