It depends entirely on what you're intending to do, but three 650s would be a pretty normal kit for interviews, yes.
It's a good idea to have a reflector, as the light from a tungsten fresnel will otherwise be very hard. They can also be used, if they have a zip-on black cover, for flagging light, and some of them zip down to become a diffusion panel as well. Yes, reflection or diffusion does absorb a certain amount of light, but that's normal enough if you want a more diffuse light source.
LED lighting is more efficient, although in most parts of the world you should be able to run two of your 650s from a single household outlet. LED is also more expensive, though, and you won't get as much output from those LEDs as from a 650W tungsten fresnel (which will be far cheaper). There's also the issue of colour rendering, although for simple interviews this is unlikely to be a dealbreaker. One side advantage of LED is that it doesn't make the room too hot!