There is a site that goes into considerable detail about the ways Knights Templar held certain numbers in great respect and built their practices around them. Such as:
The number 3 (omnipresent)
* The 3 religious vows (common to all monastic orders).
* The 3 mandatory alms every week.
* The 3 annual fasts.
* The 3 meals per day.
* The 3 meat meals per week.
* The 3 presentations of the novice before the Chapter prior to the reception ceremony.
* The obligation to accept a 3 against 1 fight.
* The 3 assaults of the enemy before the Temple’s counterattack.
* The 3 horses that the Knight Templar received when setting off on an expedition.
and the list goes on…
The number 8
* The 8 days of penitence to be suffered by a Knight Templar guilty of a venial sin.
* The 8 sacraments received by the Knights Templar.
* The 8 angles of the cross pattee humettee.
* The 8 articles of the oath taken by the future Knight Templar.
The number 9
* The 9 traditional founders of the order.
* The 9 Knights Templar required to form a commandery.
* The 9 provinces of the Temple of the West.
* The 9 years’ preparation for the Temple (1118 to 1127).
* The 72 articles (7 + 2 = 9) of the Primitive Rule.
* The 180 years (1 + 8 + 0 = 9) for which the order was in existence.
* The 9 000 Templar commanderies (unverifiable number given by Matthieu Paris).
* The 117 (1 + 1 + 7 = 9) charges leveled at the order during the Inquisition.
* The death of the last Grand Master, Jacques de Molay, also characterized by the number 9: he was executed on March 18 (1 + 8 = 9), 1314 (1 + 3 + 1 + 4 = 9).
Here is my take on this. Notice that there is a lot more things and entities listed under the auspices of number 3. It seems that 3 is just a good number for most things that are not in particularly great supply. So, there was nothing specifically “Templar” about using 3. 8 and 9, although both numbers with substantial numerological pedigree, are more difficult to come by in most cases. It seems to me that 9 was of particular importance, because the Templars for a long time insisted that there were only 9 members, even when undoubtedly daily operations of the Order required more knights and servants (who technically are also Templars).