I always assumed F!Morgan is. She is in my eyes.
None of Owain's or Cynthia's conversations with her indicate that she is.
However, none of Cynthia's convos indicate that they don't associate with each other either (Owain is scouting her as a partner in their Support Convos which could indicate a lack of closeness). She's just not a member of the Justice Cabal.
Er, no.
Default =/= canon. For example, KOTOR II set the default gender of its main character to male, and yet she's canonically female.
Robin is whoever you want him/her to be. At least Sakurai has made efforts to show F!Robin more often than the male Wii Fit Trainer or female Villager, considering that her own official render is right beside the male version.
If Male Robin is the default gender, players new to Smash who don't know about Robin will almost certainly associate Robin with the male gender.
Sakurai also mentioned that he put the different gendered Robin in as an alternate costume because that Robin would still play the same as the other one, even if appearances and gender (and voice) changed. Lucina would have been an alternate costume of Marth for the same reason (as she would practically
be Marth, meaning no need for a separate slot on the roster), but Sakurai removed the tipper which meant that Lucina couldn't be "Marth" anymore, but also paved the way for letting her be her own character and get her own spot on the roster. Given how Male Robin is the more prominent one (on his own for the face render, his official render overlaps F!Robin's, is and is featured prominently alongside Lucina in both the artwork that the artist for Awakening did AND in their trailer), Female Robin would be the alternate costume which indicate a lack of importance.
The one thing I'd like to say however is that I will retract my opinion on which gender is the canon gender and admit I am wrong if both are featured on the character select screen for the new Smash Bros. As we've seen both official renders, I believe this to be an equally viable possibility that they will both be on the slot for Robin, and it makes who's the default gender and who's an alternate costume into a non-issue.