Is Sefiras Haomer nowadays m'dorasia or m'drabonon?
The Biur Halacha cites a machlokes Rishonim as to whether counting sefira in our times is a mitzvah m'dorasia or only a rabbinic requirement that serves as a reminder of the Beis Hamikdash. The Rishonim write that since it calls attention to the fact that we no longer have a Beis Hamikdash, this mitzvah contains a trace of sadness and we therefore do not recite shehechiyanu on sefira. The beracha of shehechiyanu is typically recited only on joyous occasions. The Biur Halacha further notes that although the Mechaber and other poskim are of the opinion that sefira today is only m'dirabonon, there are many Rishonim who hold that it is m'dorasia. Therefore, he writes, it is proper to adhere to the prevalent custom of counting sefira only after nightfall [the emergence of three stars], as is generally the practice with mitzvos d'orasia that are fulfilled at night.
(ביאור הלכה ד"ה לספור; ביאורים ומוספים דרשו, 20)
Hilchos Tzitzis 11 (page 44)
The Required Number of Strings
Fewer or More Than the Correct Number
The Braids and the Knots
The required number of strings
The Torah uses the words gedilim (braided) and pesil (doubled) when talking about the mitzva of tzitzis. In singular form, gedil implies two items braided together; in the plural form, gedilim implies four items braided. Chazal understood that the tzitzis tassels should be made from four strings braided together. Pesil tell us that these four strings should then be doubled or folded over when inserted into the garment. In all, there are four strings on each corner that are doubled (folded) when inserted into the corner holes to make eight.
(סעיף יב וס"ק נח)
Fewer or more than the correct number of strings
If fewer than four strings were used on a corner, the tzitzis are pasul. Likewise, if more than four were used, they are pasul and in violation of ba'al tosif. According to some poskim, if an extra string was added after four were already tied, the garment remains invalid until all the strings are removed and the proper number is retied. Many poskim hold that ba'al tosif is violated only when a string of a different type is added - e.g. if a cotton strand is added to a set of woolen ones. This opinion can be relied upon until the matter can be rectified.
(סעיף יב וס"ק נט)
The braids and the knots
Chazal darshened from pesukim that one string should be used to wrap around a segment of the others. All that is required mid'oraisa is one double knot (so that it should last) on top, three coils, and a second double knot to hold the coils in place. Mid'rabonon, there should be four sections of coils, each separated with a double knot. Together there are five [doubled] knots to represent the five chumashim.
(סעיף יד וס"ק סה; וראה ביאורים ומוספים דרשו, 76)
If tzitzis were put a proper distance from the edge of a garment but then the hole or hem ripped enough to make them less than one kesher godol from the edge, the tzitzis remain kosher.
It is customary to reinforce the edge of a garment and the area around the hole in order to prevent ripping.
Many taleisim have knotted fringes made from leftover warp threads around their edges. This section is not considered part of the garment and the tzitzis should not be placed in this area. It is proper that the area of the corners should be free of any such fringes.