Hi and welcome to YT
Your little Kippir is little indeed
I haven't heard of small dogs dying, but Nena and Rufus are my first small dogs so I don't have much experience.
I agree with the vet on waiting untill he is full grown to have him neuterd.
Don't know how big he will be. I know there is some sort of chart where you can get and idea of how big your pup will be. Someone else might be able to help you with that