Well, it very much depends on who is available. I don't know when they decided to become nuns, but one of the sisters of Francis II of Brittany would be interesting. that's in addition to any potential French, Burgundian or Iberian matches.
I can't see this happening. I mean, even if Edward IV still dies on schedule then the landscape is totally different. For starters, that's a very big "if", seeing as the PoD is almost 25 years before that point. Secondly, if Edmund is alive, Richard is not the heir, even if he disposes of Edward's kids. If Edward still has boys, that is. Secondly, with a surviving Edward, who can say that Clarence will suffer his OTL fate? That needed a very specific set of circumstances. Even if Edward IV dies in exactly the same way at exactly the same time, the world is likely very different. For all we know, Warwick could still be knocking about! Edward of Westminster could be plotting in Lorraine, waiting to come home.
If Edmund survives, the 1469-71 period is likely to be changed utterly. If that happens, then 1483 is totally uncharted waters.