Regarding Ngan Yu Yuk,
click to show/hide spoilers I think she committed suicide because of her pride and ego. She was a survivor and believed that by her own talents, wits and looks, she could achieve her dream of becoming a famous actress. But when she became paralysed, she knew that she would be torn away from the stage and the spotlight. So after getting the best actress award, she knew that her dreamwas fulfilled and would rather die on her stage in the filming studio rather than leave it.
Also, I wish they showed more of Duen Siu Cheung's feelings towards Ah Yuk. Ah Yuk is the only person who supported him good, bad and ugly, and gave everything she had for him to have his revenge. Superficially, it looked that their friendship was based on mutual use to get what each side wants. She wanted to be the lead actress and he wants fame, money and revenge.
But I believe that there should be deeper feelings between the two - not romance but at least a deep comradery. Since Duen Siu Cheung is the only man around Ah Yuk that did not be nice to her for her body, and he did sacrifice a lot to jump off the truck and turn back to take care of her while she had the measles. And she too, treated him as a true friend all the way. She really craved that best actress award yet Duen Siu Cheung bribed the judges to give it Bak Ling instead (which I thought was a bad betrayal). She was angry at first, but then she quickly forgave him saying that she valued their friendship more.
So I really dislike how Duen Siu Cheung gets obsessed with Bak Ling when they woman standing behind him had always been Ah Yuk. But then romance can not be forced, however I do feel that Duen Siu Cheung and Ah Yuk suit each other more.