Congratulation... Welcom to TAI
The cost of Santro 2007 model for Rs.2.80 is little costly. You have decided to buy automatic, so check the usages of previouz owner. Chech the smoothnes of clutch. For long time use it is better to go for mannual.
Here are the replies for your questions:
1. It is good to have all documents photo copies while travelling. When going to Chennai if any cops asks you just manage with them simply but, don't say about name changing process. Then he may ask for all details.
2. Yes you have to change insurance to your name. It is better to do both at same time.
3. It is lettle difficult, so better avoid causing any damage to your car.
4. This can't be done.
I hop that you own it soon and post your experience.