If you can file something then you can turn it, as simple as that. Some stainless is "free cutting" and is much easier to cut but all stainless can be turned. Cutting speeds are important and HSS will cut although not as good as tipped tools. Size of lathe is unimportant so buy one that you have the space for. Remember, don't try too big a cut on too high a speed. One answer states that ss hardens as you cut, not true. The only time it will harden is with excessive heat generated from a tool that rubs stock away rather than cut it and you should always use a small amount of coolant anyway as the cutting action itself will generate a certain amount of heat. When I have finished turning anything I can touch it with my bare hand so the heat generated is only minor. Your turnings should be the same colour as the stock, this is always a good guide on how much heat is being generated. All the above is a general rule and by no means definitive.