MB 71: At the end of every string - Look previously in MB 18 what we wrote there. It is proper to make the strings of medium thickness - not thin and not thick because of "this is my G-d and I will beautify Him." (The standard sorce for beautifying Mitzvos.)
11:15 There are those that say that one is required to hang the Tzitzis (72) along the length of the Tallis because the Tzitzis (73) should drape the edge {this means that they should hang from the edge} and if they are on its width they won't be draping the corner because they are hanging towards the ground. There are those that say that one should not place (74) any cloth in the holes, of the Tallis, that one places the Tzitzis in (75) and there are those that permit this and the custom is according to the second opinion.
MB 72: Along the length of the Tallis - Look earlier in MB 52 what is considered the length and look in the Beur Halacha (where it is pointed out that the length is that direction which is wrapped around the person and the width is the dimension that is along the height of the man. However there are those that question this - that when the Tzitzis are put along the length of the Tallis, the upper two Tzitzis will not drape over the corner of the Tallis and they therefore state that it is better that the upper two be along the length and the lower two along the width of the Tallis. However, this is all the optimum but even if they are not draping over the corner the Tallis is still fine.)
MB 73: Should etc. - that is at the time when the Tzitzis are attached or at some later point if they move to the bottom of the Tallis he should return them. All this is a priori, but post facto there is no strictness. However, one should be very careful that the Tzitzis should not hang directly on the corner at an angle because this was the Karaite (those that rejected the Oral Law) custom and if they are hanging like that it is a Mitzvah to move back to the rightful position.
MB 74: Any cloth - Because we require that the Tzitzis should be placed on the corner and not on something that is placed on the corner.
MB 75: And there are those that permit - Because this is only done to strengthen the garment so that it does not rip and it is ancillary to the garment, and even if it is made of leather (which doesn't require Tzitzis) it is permissible and the authorities agreed to this.
Binyamin Rudman