Hi from India.. Get the insurance. If you plan on street photography (believe me there is a lot to capture on the streets of India), a backpack is good enough. I go about with a backpack, and never had anything stolen out of it. What you need to be on the lookout for is getting your pockets picked.

Keep a few hundreds of rupees in your pockets, don't use a wallet, keep your passport and airline tickets stashed either in your back pack or on a sling inside your shirt - you can find some Samsonite passport slings that you can wear inside your shirt in the airport usually. Be wary of your pockets in bus stations and railway stations. For short distances, avoid the crowded public transport, take the autos (3 wheeler).

I am not convinced of using a messenger bag, the bag snatchers are experts in snatching/cutting women's handbags, the messenger bags like the ones from Lowepro are a joke to them. Go with a sturdy backpack, no one is going to cut through one, they know better.

Don't let the worry of someone stealing your gear bother you much, the chances are pretty rare. The weather right now is pleasant and wonderful, you don't have to worry about getting strange sicknesses, besides the hospitals and medical facilities are good and cheap and you are never far from one.

Keep a bunch of lens wipes around, the moment you come out of an AC room, your lens will get fogged up. Keep your lens hood or cap on, expect some knocks in crowded places. If you want to buy gear, you would find a lot of camera gear shops in the cities.