Chennai Experience: I have been to Chennai in summer. I visited Marina Beach on a Saturday and it was full of crowd. I enjoyed Horse ride and the beach was great.
However, as you are at see shore, it was full of sweat and I used to bath thrice a day.
Food, sight-seeing and shopping: No Idea.
Activities & things to do: Visit Beaches.
Travel tips, How to reach, travel warnings etc: None.