Too many generalizations here, I contacted e coli in my second month in US from canteen food in school, India is a sub continent and therefore variety is everywhere as language, food and cultures differ hugely from state to state. South is hot, North is bitter cold in winters depending on where you are, India has the coldest regions in Kashmir, Himachal and some of it seeps into Delhi as well during winters, this is due to the Himalayas.Food varies as well, from over-spiced and hot south Indian crude offerings to delicate and aromatic north Indian offerings which draw the likes of Gates, Clinton, Putin et al and easily blows away the much vaunted French cuisine or the limited scope Chinese and other Asian cooking as well.
As for terrorism, it can happen anywhere so that is entirely a matter of chance, good to avoid crowded places during festivals etc. As for street food, avoid it at any costs, only go to proper places, don't miss Bukhara restaurant in Delhi if you are there, India is 6000 years old, so bear with it, no sweeping changes here so there is a mix of old and new living in compromise. As for tourist spots, there are too many to fill in few weeks but prioritize, and you will be a happy camper. If you like ancient 4000 year old forts and construction, then North is for you, if you like to see the Himalayas, again north is for you and watch out, its cold here now. If you like tropical weather and myriads of ancient and new temples, south is for you then, I am not too fond of their food but as people, they are more receptive than north.
Lastly, don't be a scared tourist and go into a cocoon, that way not only you loose out learning, you also get into the classic tourist trap and get fleeced as well. So enjoy and if you need any more tips, send me a PM.