1: An ICC profile is essentially a "color filter", nothing more.  You (the user) need to know how and when to apply it.  That's why every profile comes with instructions on what printer, paper, ink, media type to select, driver quality, and other driver settings to use with that profile.  If these instructions are not provided with the profile, the profile is useless.  Think of it like buying batteries.  If you buy AA batteries, you are responsible for knowing what devices to which they apply.  If you try to stuff a AA battery in a smoke detector that uses 9V batteries, that's on you.

2: The answer is in the name of the selection: let printer/driver manage color.  If you set this selection, the driver is responsible for applying any color corrections or profile (not Qimage).

3: It simply sorts existing ICC profiles be relevance, taking into account the printer, media type, and the name of the ICC profile.  So profiles with a name that matches closest to the printer and media type will be near the top of the list.

Regards,
Mike