I've no idea why it would ask about gamut - it's just another native monitor color space; they're all a bit different anyway. Why would the calibrator even care? It should just read the values and make the profile accordingly and not have any opinions beyond that...are you sure you read that correctly?
No, don't use the supplied profile. It's probably all over the map, most canned profiles are, and it certainly won't be anything close to accurate.
The "express" edition of the Spyder is a bit limited software-wise, but the sensor is top-notch (same sensor as the other editions, just cosmetically different). It has no problems with wide gamut monitors.
Just be aware that it does not support a multi-monitor setup. You can calibrate one display, and that's it. Additional displays should be left alone to use sRGB. If you attempt to calibrate another connected monitor, the same profile will be used for both. Which makes it pretty useless in a laptop + external monitor setup.