Hi! I'd like to point out a few little things that just came into my mind...
I don't have any kind of experience with identical twins, and even though JKR did say,
QUOTE(Moon(I luv you Luna))
Fred and George were "Identical to the very last freckle"
I like to remember that they both have very different personalities, and anyone who spent a reasonable amount of time with them was able to tell them apart, among them, Alicia and Angelina.
Both girls not only spent their lessons for 6 years with them, but also were on the Quidditch team, and were very aware of the differences between both twins. I don't really think that the whole incident of Angelina ending up with George was something that came out as planned or to just "replace" the other one. I don't really like that match, but I give the girl more credit than to say that...
Yes, I would have liked it so much more if George would have ended up with Alicia, and I believe this probably happened because they were friends from the beginning. Of course we would read that the twins would hang out mostly with Lee, but I don't know why it's easy for me to fit Angelina in the picture of their mischief-making as well. Does this happen to any of you guys as well?
I don't really think that Fred had a serious relationship going on with Angelina, I think he did like her, as much as to ask her to the Yule Ball, not really as much as to date her, that's why I forgive George for marrying her in the end, mostly because they were all friends.
Now, the kids thing. Yes, another would have been nice, what about twins too? They are supposed to come on the male side, and there was a hole there for me too. I don't think the financial thing was an issue for them, maybe they just didn't want a big family, or maybe he did have the fear of going broke eventually because of a big family... Maybe he was afraid of having to handle kids as troublemakers as he and Fred were... Who knows.
Still I feel like JKR didn't give this a lot of thought, especially since she got the date wrong for Fred's death (it should have been 1998, not 1997.) Just like
Moon(I luv you Luna) said, I'll also stick to it since it's canon, but I'm not really happy about it. Fanfiction can always provide nicer results, at least for me.