For bowl turning, you need to slow it down. For 16", you will need to slow it down a lot. A small side effect of that is a less powerful motor becomes a bit more torquey (horse power isn't what you want, it's toque). Ther question is are you going to be making bowls out od exotic woods, like iron wood? That stuff dulled my wood chisels badly.
If you are doing the really hard woods, a 1hp motor should do nicely. For wood, I don't think you need much more than 1hp. Overkill doesn't always hurt (unless you get a chisel in the wrong place). My 1/3 hp motor does fine for smaller diameters. Do you have a regular wood lathe? You might be able to build something off of the back side if the spindle to handle bowls, depending on threads.
joe