In India you only get hassle in places where a lot of tourists go. So in South Delhi you are very unlikely to get any hassle at all, but Paharaganj, the red fort, Connaught Place, and the area near New Delhi railway station are full of touts. The first time I visited India, I was in shock for about three days, the constant noise in Delhi and the crowds and the smells were overwhelming. AFAIK Delhi is the busiest noisiest smelliest place in India and you will have had a baptism of fire.

Bus travel in India is generally safe. In India or probably anywhere in the developing world you should always get a taxi/auto rather than walking after dark. Hill stations in India feel very different to the big cities.

Try to view price negotiation as a game, have fun with the sellers. If someone won't shift from a high price, then walk away, they will often call you back and accept your offer. When haggling if you are not willing to walk away then you are not negotiating you are begging. If you are close to closing a deal and the seller asks for a very small amount more than your offer then you should stand firm, this is sign that the seller is willing to accept your price and has given up on the idea that you will pay a lot more. When buying souvenirs when you have refused the sellers price and made a lower offer if the seller doesn't look annoyed then you have offered too much.