Is there any gameplay difference between Coco and Crash?
After the first boss in Crash Bandicoot (in the Crash Bandicoot N. Sane Trilogy) you're able to swap to Crash's sister Coco.
So far it seems like both have the same abilities and movement/attack speed. Is there any difference between them at all, like locked level parts for either of them? Or is it just a cosmetic choice?
It's a cosmetic choice - Crash and Coco share the same physics. While some levels specify that you have to play with either Crash or Coco, you don't have to play a level with both Coco and Crash to be able to get everything in it.