I would not worry about supercharging, we just finished 7100km trip to Phoenix and back to Burnaby. We saw more Teslas on delivery trucks than we ever did at superchargers. The trip planning helps work out the kinks, we stayed mainly along the supercharger route through Salt Lake City down to Phoenix. The unpredictable wind factor was our only real concern, we may have lost an extra 7 to 10 % some segments. Returning along the I5 northbound was very predictable, we could have easily managed with the cars 10% buffer.
Let me know if you need any suggestions while the trip is still fresh in my mind. CF