Well let's see, Gen-X Cops was '99, and Dragon Tiger Gate came out this year, which means he's had rougly 6-7 years of evolution there, doing other action projects like A Man Called Hero, Time and Tide, My Schoolmate The Barbarian, New Police Story, etc.
And I believe the styles he practiced were Muay Thai, Taekwondo, Northern Shaolin kung fu and Changquan, but I'm sure there were more, and I'm also sure he picked up a lot from Donnie and the other stunt veterans on set.
Tse is actually one of my favorites of the "pop star action hero" generation. He's a really good actor, learns quickly and takes it seriously, and his hair is always perfect. Damn that hair.