Well-said! I was thinking the same thing about points 1,4 and 5 while watching the drama. Agree with the other…
It's not based on a real life relationship. The author died, which is where I think that you have your wires crossed. Whomever told you that didn't have their facts straight. The author's widower actually gave them permission to continue with the story and even told them the ending that his wife intended, so that the anime would follow her intentions, even though she couldn't finish the manga herself. https://icv2.com/articles/comics/view/14171/dmp-acquires-itazura-na-kiss
My main question is: where did Danyi's daughter went?! xD
pratyasha is right; she was sent to school in the Philippines because she was being bullied at her old school. She was sent abroad so she wouldn't have a hard time. Also, remember when the show started, Dan Yi was homeless so I'm sure that played a huge part in keeping her abroad. Eun Ho originally let Dan Yi live with him so she could save money and get a place of her own. So, even then, her living situation was temporary. It made sense to keep her daughter out of the show.
https://icv2.com/articles/comics/view/14171/dmp-acquires-itazura-na-kiss