With the regards to the Raavad wrapping... In the non chulya area are there any rules at all? Could I, lets say, wrap 20x - or is there still minimum of 7 and max of 13?
The idea of “minimum 7 and maximum 13” applies specifically to chulyot – as stated by Rebbi (Men. 39a).
According to the Raavad (see https://www.tekhelet.com/diagrams/RaavadTyingSource.htm), the statement of Rebbi refers to the wraps of the chulyot (as opposed to most Rishonim who understand Rebbi to mean the number of chulyot which are each three wraps). So he requires each of chulya to have between 7 to 13 wraps. The Raavad explains that there are to be 3 such chulyot within 5 knots.
Given that 5 knots leaves four sections between them for wrappings, three of the sections are occupied by proper chulyot, the fourth section not being considered a real chulya per say. As such he explains that one can wrap however one wants in that section.
To be specific, in his hasagot on the Rambam he writes one can wrap blue or white however he wishes, but in tshuvot he writes “dak dak” which has been interpreted to mean white only. It is my personal recommendation that one tie only white there in order to emphasize that the area is not a real chulya.
Regarding the number of wraps in this section, the Raavad makes no mention and it seems clear one can wrap as much as one sees fit. It is my recommendation that this area be wrapped with the same number of wraps that are used for the real chulyot for then one fulfills the Rosh’s recommendation that all the wrappings being equivalent.
Furthermore, even if one wanted to wrap some other amount, one should be careful that the total wrapped and knotted area of the tzitzit (gdil) is precisely one-third of the total length of the tzitzit (i.e., gdil and anaf), in order to maintain Rav’s l’chathila requirement of shlish-shnei-shlish (see https://www.tekhelet.com/pdf/ShneiShlish.pdf).
– Mois Navon.