Have you driven this yet? TSX's with automatics feel very sluggish. I would recommend the 6-speed.

To find out what you should offer, check KBB and edmunds and autotrader/cars.com. Find prices for similiar mileage, then lowball them and start the negotiating. Remember that 'certfied used' doesn't really mean anything to you when the car still has 35k miles left on the factory warranty.