ChrisH I am so excited that you are going to get not one but two cats!
You have been a great dog mom and bird mom, I am sure you will do fine as a cat mom as well! I think cats are easier to care for than dogs and you already know how to care for a dog.
About the indoor only thing, it will be easier if they are young but have you looked into leash training the cats or do you have a fenced in yard for Bob that the cats would be safe in under your supervision? Those are two choices to consider in case they are not happy as indoor only cats.
I would suggest when you first introduce Bob to the cats have him on a leash or in his kennel until you know what his reaction will be to them. I am sure other pet talkers who own both dogs and cats can help you with more advice on how to introduce them.
Please tell us more about Suki and Suzi. What color or breed are they? Do they resemble any pet talk pets? I am so excited for you! Don't worry about asking too many questions, pet talkers are here because that is what we like to do, talk and talk and talk about our pets!