Question

I have, thank God, started putting tekhelet into my tzitzit. I have three questions:

1. In a case where the person who prepared the tzitzit did not say beforehand, “for the sake of the commandment of tzitzit,” are the tzitzit considered to have been tied for their proper purpose and therefore valid? After all, there is no reason for a religious person to make tzitzit not for the sake of the commandment, right? Or is there some technical requirement of “for its proper purpose” that specifically requires an actual verbal declaration?
2. I tied them according to the Vilna Gaon’s method, and in some of the windings I made a mistake and did only two “stripes” instead of three (as a winding is supposed to be made). If I undo the tzitzit knot, I am afraid the tzitzit will be significantly damaged. What is the status of the tying? Rabbinic? Custom? Does the above mistake invalidate it?
3. Does the Rabbi prefer one of the tekhelet tying methods over the others from the standpoint of reason and logic?