We need to revive the Bay! turtles and the fandom
Michelangelo can breakdance (best and first move was the spinning on your back one), also a great hiphop dancer. He will listen to music and dance without noticing, almost choregraphing for the song itself. Will have dance offs with his brothers. Sharp angles but great body control as well.
Donnie will try to engineer new things, it's canon he made vegan pepperoni or salami, so I imagine he does this with a lot of stuff. Will and has tried to make vaccines, accidentally made a new disease once, yikes. Has tried to reverse engineer so. many. things.
Leonardo was a MASSIVE snitch when he was younger. Like say you don't wanna train once in his earshot and Splinter already knows, kinda grew out of it.
Raphael once ate 12 pizzas in one sitting, much to the dismay of Leo, Donnie and Splinter
The lair has showers as well, they obviously remove all gear for this. Michelangelo has the worst hygiene, often being reminded to clean every shell crevice by Donnie and Leo. Donnie goes full nerd science mode with explaining possible illness or infection and to be careful, Mikey never listens but somehow doesn't get sick often.
Absolute shenanigans occur in the lair, they all have hobbies to combat the threats of the ha-shi.
Mikey does anything creative, music production, sketching, skateboarding, anything. Will often learn dances or raps in his free time.
Leo likes classical literature, both Japanese and Western, he will watch video essays explaining every little detail. Also likes to cook as well, makes a MEAN bowl of ramen (homemade broth, chashu, everything)
Raph often has to compromise his strength for speed and agility, so he sometimes does speed and agility courses. He also does beat boxing and rap, writes and records his own with Mikey.
Donnie stays on top of science research, will read the newest papers. Although, he does like to also collect trinkets. Think figurines from TV shows or video game characters, all trinkets are from franchises he likes and plays/watches.
Also I feel like be Native American, because they're red eared slider turtles, which are native to America. The species is native to central and southern USA and northern Mexico.