
I own a bull terrier boy & patterdale/staff x lab girl and 2 cats. When I got my boy the breeder told me they would never get on with cats he was very wrong! I had 2 older cats and they hated dogs ! As he was a baby only 6 weeks when I brought him home he really couldn't get near them as they were much faster + wisher they just get out his way. my one cat did used to wait until he was asleep then dive on him and start beating him up but she was a old nasty cat!
When I got a new kitten snoop my boy was very in its face he was 6 months old so held on to his collar all he wanted to do say hello and give him a good sniff.
The most important thing for a while at least is never leave him/her alone with the cats as they might gang up. Is it a girl or boy your getting ?
Stroke the pup then stroke the cats by transfering their smells they become used to each other much quicker your cats will not like this and will quickly move away and groom themselves to get rid of this new odd stink of dog

. Feeding them all at the same time will get them used to each other and teach your pup that cat food is not his! Make sure you give your cats lots of cuddles in front of your pup. You don't want them to end up resenting the new member of the family.
As they are only young too they will all soon get used to each other. My terrier mix tinkerbell plays rough house with my cats and gets beaten up but loves them dearly.
My cats now even come for a walk with us which is great until i see another dog ;0