1: diamox for ASL 3000m for tourist traveller is pretty common advice from a doctor. and that was the exact advice i received when i started.
3000m has about the same pressure as a commercial airline cabin. Most people on a commercial flight do not take diamox. You say a basic guide is to use diamox at 3000 meters. This isn't true in any place I've climbed. Did the doctor also recommend it when flying a plane?
When did you start? Who was the doctor? What mountains have you climbed? This information could be useful.
3: 7000m for professionals, definately. for ameteurs, i doubt so
I know it has been used before (even on Denali), but rarely. Please show us one expedition to a 7000 meter peak that uses supplemental oxygen for anything but emergency use.
Here are the two most popular 7000 meter peaks:
http://www.bing.com/search?q=climbing+l ... b008fd6778
http://www.bing.com/search?q=climbing+m ... &FORM=AWRE
Even on all the guided trips that I know of, they don't use supplemental oxygen. Can you show us one expedition, guided or otherwise that commonly uses it for an 7000 meter peak?
(Note: Sometimes it is used for sleeping on peaks like Everest at not that much over 7000 meters, but that's an 8000 meter peak and they don't use it just to climb to 7000 meters).