Not sure if you'd need the Receptor with that kind of set up - as you could run the VSTs out of Ableton. People normally use a Receptor when they don't want a computer involved at all e.g. running VST synths like Reaktor or Massive straight from a master keyboard.
Whether you need an audio interface or not depends on a) are you looking to record high quality audio, or multiple tracks at once and b) how 'heavy' your tracks are. An audio interface can take some of the strain away from your CPU, but the best thing is to see what you can get away with without one, then work out what you need.