Hi,
A big welcome !
September and October are good months to see India in its best. They are dotted with festivals that I am sure you will enjoy. End of September in fact sees biggest Hindu-Bengali festival called Durga Puja. Post that there are other festivals lined up as well. Another worth mentioning is the Dasara in Mysore. Seeing Calcutta during Durga Puja is an enriching experience in its right. The pulse of a place can be best felt through its place, festivals and food.
You can check the following links to have an idea :
Mysore : http://mysoretourism.org/highlights.htm
Mysore :http://mysoretourism.org/mysoredasara.htm
Durga Puja :http://www.calcuttaweb.com/puja/
Ladakh will not be an issue at all around September. In fact that’s one of the best seasons to go over there. India is a land of extreme and often conflicting climactic conditions. August and September get rain no doubt but not the entire country.
Following is the link of a club I am part of. This is to show that there are many people who will be going to Ladakh-Leh around the same time.
http://tagindia.blogspot.com/2009/06/tentative-schedule-ladakh-driving.html
I would say India is a land of extremes and yes I am sure you would find cows here and there but trust me its more than rope tricks and elephants and outsourcing. I am sure you would love the country in your own way. Time is a constraint so all the places cannot be visited within a short span of time. I think Svein , you will like the following places :
Delhi-Jaipur-Agra-Rajasthan ( History and culture and food )
Haridwar / Varanasi ( Religion and history )
Goa and its surrounding ( Sea , nature , beach , spa , food)
Hampi (http://www.hampi.in/) ( Ruins of ancient kingdoms )
Kerela and parts of South India ( depends on the time you have )
Calcutta
Sikkim and Gangtok
Nepal
Keep in touch,
Best wishes,
R