The pump I use and recommend is a 12V submersible water pump that I picked up at Clas Ohlson in Norway. For a water reservoir everything that can hold water can be used. I choosed a cheap Tupperware box. The box is then filled with water, closed and sealed with waterproof silicon. If you plan using ice cubes in the water you will also have to insulate the box itself.
Copper is preferred as coldplate material because it removes heat faster than aluminum.
Thickness, 2-4 mm. Make it to fit the Peltier elements size perfect. It is also a advantage if you use insulation that is easy to cut and work with. I use a easy system that everyone can make. Take two 2mm plates, drill holes in every corner and tap one off the plates.