Sure.
Cool. Same (Sorry Spartan)
Basically, it depends on your oath level. The higher your oath level, the more control you have, and the less investiture you use. For instance, at oath level 1, you could probably control 2-3 ribbons of wind with some strength, for a few minutes - with the power of one crystal.
Oath level 2, probably 4-5 ribbons of a bit more strength, for a bit longer, etc.
Of course, ribbons of air isn't the only thing you can do; you could probably make a shield or knife out of the wind, and that would be less/more durable depending on your oath level.