I would get the bottoms as well. I wear both and once I put them on, I rarely take them off until my trip is over. I've worn them as outerwear with a pair of nylon shorts over the bottoms. Mine are Patagonia Capilene.

I would take a water bottle for sure. Better yet, a water bottle and a Thermos or similar steel insulated bottle. Mine is sold by Liquid Solution, costs about $20, keeps hot liquids hot for hours.