Really cool! I like this interpretation and design of the character and how he looked more like a zombie as one comment said. I actually had an idea for the characters playthroughs too.
Sonic would be the easiest to play with due to him, well, being Sonic. The shonen anime type of guy who will kill gods, the freaking End, and maybe Solaris if you count him later on in his life and deals with eggman weekly. Although the stages would be a little harder. And of course a gruesome death if you die. But overall not too different of an experience from normal Sonic due to Sonic's experience.
Knuckles would be a little harder than Sonic due to him not dealing with Eggman 24/7 and his more serious personality. Kind of an inbetween difficulty between Sonic and Tails.
Tails would be the hardest. I mean, dude is literally 8 years old trying to survive. It would be like the stealth missions in Spiderman PS4 where instead of being a shonen anime protagonist, you're some normal person trying to not die