I don't have the specifics of why you would require 2 modules exactly you may have to check that with TAC directly its most likely something to do with the architecture or a best practice , I just know what the F & M modules numbers and letters stand for in the platform name as I have researched them before for my own kit
i am sorry to differ here:
23 - 2 refers to the type of fabric module it has. here, it is equipped with Fab 2 fabric card.
3 refers to the minimum no. of fabric modules required to operate at its full capacity. yes, you can have only 1 fabric card but to achieve full bandwidth of this linecard, you require 3 fabic modules.
sorry. i edited and corrected the mistake. in Nexus 7k, each linecard will also have a fabric in it. the 1st number refers to the fabric the linecard has. so, if you install F1 fabric card in the chassis and use F2 fabric linecard, the linecard would operate as F1.
yes, you are right in terms of channels.