The Shulchan Aruch (11:1) writes that one must verbally declare when he begins spinning the wool that he does so for the purpose of the Mitzvah of Tzitzit, and the Mishna Berura (11:4) clarifies that one must make this declaration verbally, rather than merely having this intention in mind. The Mishna Berura is uncertain, however, whether Bedi'avad (after the fact) the Tzitzit are invalid if one had this intention in mind but did not verbalize it.
The Rama (11:1) brings a view that requires having this specific intent when combing the wool, but observes the common practice to be lenient in this regard. Nevertheless, as the Mishna Berura (11:3) mentions, the Maharal of Prague held that optimally one should comb the wool specifically for the purpose of the Mitzvah of Tzitzit.
The Shulchan Aruch (11:14) records such a practice, and the Rama (11:3) advises that this be done. The Mishna Berura (11:18), however, cites opinions forbidding tying knots at the end of the Tzitzit strings, and rules that one should refrain from doing so if the strings are properly woven such that unraveling is unlikely to occur. The Arizal permitted tying these knots. The Halacha Berura cites an opinion permitting tying these knots provided that one does not do so on the same day as he ties the Tzitzit to the garment, so that he does not give the impression of adding onto the Mitzvah. In any event, nowadays Tzitzit strings are generally woven very well, and it is therefore advisable not to tie these knots. Nevertheless, those who wish to tie the knots have authorities on whom to rely, but they may not do so on Shabbat, as this violates the prohibition against tying permanent knots on Shabbat.
One may cut the Tzitzit strings to shorten them after they are tied to the garment (Rama, 11:4); however, one should preferably not cut them with a metal instrument, but rather with his teeth or other non-metal instrument (Mishna Berura 11:61).
The Shulchan Aruch (11:4) records two views as to whether the strings must be a minimum of four Godalim, or twelve Godalim. Common practice, as the Shulchan Aruch notes, is to require a length of twelve Godalim, or approximately 9.5 inches. The Mishna Berura (11:20) clarifies that this length is required beyond the point of the first knot tied against the corner of the garment; the part of the Tzitzit that extends from the hole to the edge of the garment does not count towards the minimum required length of twelve Godalim.
The Shulchan Aruch (11:6) disqualifies Tzitzit strings produced from stolen wool, whereas the Rama (ibid.) holds that although one should preferably avoid using such strings, they are not disqualified. The Mishna Berura (11:30) brings a debate as to whether the Rama's ruling applies even before the wool's owner despaired from retrieving the stolen goods. According to one view, if the owner has yet to despair, then even the Rama would disqualify strings produced from this wool for the Mitzvah of Tzitzit.
Yes. However, the Halacha Berura (to 11:6) writes that it is laudable to ensure to pay for the Tzitzit in full before using them for the Mitzvah. Additionally, the Mishna Berura (11:27) writes that if the seller repeatedly asks the purchaser to pay and the purchaser refuses, then legally the Tzitzit do not belong to him, and he therefore does not fulfill the Mitzvah with these Tzitzit.
The Bet Yosef (cited by the Mishna Berura 11:39) records such a practice and discourages it, seeing it as an expression of arrogance. The Mishna Berura, however, records divergent customs in this regard and encourages each community to follow its traditional custom.
The wool on an animal at the time it was worshipped is certainly disqualified for use for the Mitzvah of Tzitzit (Shulchan Aruch 11:8), but the Mishna Berura (11:37) cites two views as to whether one may use the wool that grew on the sheep after that point.
Yes, so long as it was initially tied at the required distance from the edge (Shulchan Aruch 11:10). Nevertheless, the Rama (ibid.) records the practice to add material around the hole as reinforcement, to prevent the hole from expanding. The Mishna Berura (11:51) explains that although the Tallit does not become disqualified if the hole expands, it is still proper to avoid such a situation lest onlookers wrongly conclude that the individual is wearing an invalid Tallit.
The Mishna Berura (11:66) writes that in such a case one should simply wrap the long string around the others three times and then tie a knot (a "knot" being a double loop), which constitutes the basic "tying" of Tzitzit required on the level of Torah law. Preferably, he should also tie the initial double knot before wrapping the long string around the others.
Chacham Bentzion Abba Shaul writes that the accepted procedure is to wrap seven times after the first knot, eight times after the second knot, eleven times after the third knot, and thirteen times after the fourth knot.
The number five signifies the five books of the Torah, and the ten knots included in the five double knots is symbolic of the ten Sefirot the ten emanations of G-d's glory through which He is manifest in the world (Mishna Berura 11:65).