Schaumburger:
My current cat [Omega] is at least #9. When she came into my life some 18 months after her predecessor [Beta], I didn't make any special effort to clean ("sterilize") litter boxes or beds. Maybe it's the time gap, but she showed absolutely no signs of being "freaked out" because there were feline odors around!
She doesn't even pay attention to the couple of places where Beta rubbed his chin against a wall corner.
And, I have carried her to the vet in the same carrier in which I carried Beta when it was time to put him down!
My gut says, don't stress out about this. Just find the kitten who tugs at your heart and adopt it right away!
Hope we'll see you, soon.
SWR