Speaking of the curse... Did the Angel writers forget all about it when they wrote the storyline of him and Cordelia falling in love with each other? Wouldn't Cordelia show some caution when falling for Angel and wanting a relationship with him because of the curse and seeing what she saw when Angel and Buffy fell in love and felt total happiness? Or was Cordelia content with having a love with Angel that couldn't hold a candle to the love he had with Buffy. I just don't see Cordelia accepting his love for her NOT being forbidden enough to remove his soul. For arguments sake I will say that maybe because Cordelia became a part demon the curse only worked if Angel felt love and total happiness with a human. I guess all bets were off with his feelings for other demons much like his love he felt for Darla.
I think he talked about, on AtS, that one perfect moment of happiness is so rare that it wouldn't mean he couldn't be in love with Cordelia or have a great life and relationship. Maybe he would never be able to have a moment of true happiness again because of the knowledge that he would go all Angelus on everyone.
I want to respond to other things in your post, too, but I have to get back to raising children. Will try to respond more later.