A ribbon mic for flute is quite an interesting choice. Might sound great, however you should be careful not to get too close to the mic: ribbons tend to be very sensitive to air flow. Now, it depends what you mean by "solo" flute;
- if you mean classical solo pieces than a larger distance is not a problem, however using just one mic will never give a very full room sound – typically not satisfying in such recordings, this can of course be made good for with digital reverb but I prefer a real room, provided its acoustics are ok.
- if you mean, flute solos for rock music then you need a reasonably close microphone. As I said, that's a problem with a ribbon, but you could try to use a pop killer like singers often do in the studio. I've never seen this for flute, but it might work.
If you're just starting with recording, I'd recommend something more conventional. Get two small-diaphragm condenser mics, these allow for all kinds of recording setups, close miking, stereo room miking, whatever you want.
I've never used the cloudlifter. This is certainly not a bad idea for ribbon mics, but it can't really be better than a good general-purpose microphone preamp.
With condenser mics, even lower-quality mic preamps should give you as good SNR as a ribbon mic with any preamp.
The Apogee Duet is certainly a good device, but I know it as pretty much a specialist for low-latency audio output only (like keyboarders need live when running VST synths), so I wouldn't recommend it if you only want to record acoustic instruments. Get something with good preamps and ADs; RME is great in that regard but even the cheaper models by M-Audio or Tascam are pretty ok (not for ribbon mics without external preamp, but for condensers all right). Of course there's nothing wrong with the Apogee, either.
The Macbook Air is hardly the ideal recording laptop, but if you only need to record one instrument this pretty much doesn't matter at all, a 1998 Pentium II would be just as fine. Perhaps most important is a quiet fan and clean power supply, any Mac is usually ok in that regard.