Here's my take.
5: A super fast electric number, more faster than O and P combined. And can teleport, mega jump, use electricity and create tornadoes. He's a buff dude with a full set of muscles.
6: The anxious number who uses ice as her main ability, along with ball form, plasma, an excellent digger, icicle spikes, making bombs and invisibility. She looks like a fusion of 1, 2, and 3. She's part squirrel, part scorpion, and part hedgehog. She also uses her hair as a weapon.
7: He might look very small and harmless, but you'd be scared of what he can do, he can spit acid, have a harpoon for a tail, wall climb, use his metal teeth and a tongue mouth to bite through everything, hypnotize or disguise as other letters, has retractable wings, and the most dangerous of all, he mutates himself growing to monster size. All powers fit for an assassin.
8: An octopus spider bear hybrid, he has a hyphen on his head, and a black widow markings on his back. He's a single number who's always aggressive and angry. He can have powerful brute strength, spawn tentacles and spider legs, shoot webs and ink, latch on any surface, and create traps.
9: the most cutest cat ever. She's got a robotic armor that looks like a bottle capsule, but her actual body is slimy. She can phase through anything with her phantom like slime body, shoot lasers with her green eyes and tail, use a telekinesis beam to levitate objects, and heal someone, elasticity, shapeshifter(she likes to mimic 6 the most.), She'll regenerate a missing piece of her, if someone eats a missing piece, they get healed immediately. (she smells like strawberry donuts, don't tell 7.)
0: a cyborg planet with a rocky, techno surface. He uses a force field that only allows numbers. He has a red zone that destroys planets with one blast. Planets with life either surrender/enslaved, or die instantly by 0's laser.(Z's inverted colors)
Bonus:
Derf: a defective abomination with five teeth and one ingrown tooth. It has all the powers of 1-9 and is very unstable.