The sautè pan has straight 3" edges while the fry pan has sloped 2"edges. The sautè is good for cooking dishes with liquids and sauces. Our sautè pan includes a tight lid.
We think 11" (28cms) is ideal. It fits on most stoves and cooks meals for two to four people. Most cookware sets end up on the top shelf.
We find that one fry pan and one sautè pan with lid is all you need for a small household.
9" fry for reheating and quick meals, 11" fry for general use, 11" sautè for daily entrees, 11" Dutch oven for special meals and stews.
Any old pot will do for boiling water. A steel pan is adequate.
It is not recommended but we do it anyhow.
Copper will tarnish. Use a copper cleanser once in a while. Cook at moderate heat. Do not use sharp objects i.e. steel knives. Use a wood or soft spatula - not steel.
The aluminum core has similar properties as copper but is lighter and has more heat capacity. A Belgian company, Falk Culinair, has a patent on the two ply copper. Using Aluminum really cuts down on the price while having negligible impact on the quality or performance.
It is as good if not better than Mauviel, Bourgeat Falk Culinair and costs a third as much. Most pans are 2.5mm thick (compared to our 3.5mm).