for female the wound is tiny n sewn up, jz make sure cat dont sleep in the litter.
male cat open wound but no problem, jz make sure dont sit on the litter.

I use shredded newspaper. Replaced the shredded newspaper everyday. The reason why dust-free litter is to prevent infection. I wouldn't use crystal litter either.

You can find lots of information on pre- & post-surgery care on the internet. For female, it can take from 1 to 2 weeks for the wound to heal. For male, I usually already let it out (from the cage, not the house) on 3rd or 4th day after surgery. I caged my cats after surgery to prevent them from jumping or running.

looks ok.. but if u want some reassurance check with vet or watsap vet the pic. 

dont let kitty lick the wound.

apply antibiotic cream if provided.

It look swollen. You should bring your cat back to vet ASAP.