How to introduce dog to our cat without stress

Hi. We have had our Lily Cat for a couple months now and she fits right in with our family! We got her without knowing she was pregnant, and she had her kittens 3 weeks ago, is doing wonderful with them. We are now buying our home, so will be bringing our Rottweiler (Rose) inside to live with us. (she's lived outdoors only) She is 6 mths, still a puppy, but a large dog. I am worried about stressing Lily out when we bring her in. I am going to wait until we have rehomed all her babies so she doesn't feel Rose will harm them. What is the best way to go about this? Rose will not have had obedience classes before hand, though I do plan to enroll her in them. I plan to have her on a leash, while outside of her crate. Should I put Lily in a room by herself while I let Rose in for the first time to check out the place? Would it be ok to then put Rose in her crate and let Lily out of her room to find Rose in the crate? Or have Rose on the leash and someone else let Lily out of her room? I have no idea how Rose will react...probably bark.

One other issue I have is fleas. Lily has had two doses of advantage, and I am going to treat Rose while she's outside soon. I have seen a couple on Lily...can someone tell me the best Carpet spray to get to kill them?? I'm going on a vacuuming spree tomorrow and want to spray first.

Thank you for any suggestions!!

Definitely wait to introduce her until the kittens are rehomed.... because you have no idea if Rose would hurt the kittens or not. Has Rose ever been around cats before? I'd do introductions super slow. I would say maybe have Rose on leash but have very good control of her. They aren't going to be BFFs at first but things should work out if Rose does not have a prey drive. Just know that Rose is not fully mature so she could have prey drive in the future. So I wouldn't leave them alone together until you absolutely know they get along.

I've never had a problem with fleas so not sure what carpet spray to use.

Rose has only been around one cat at my in laws, one or two times when younger. She was scared of it and their dogs, she's really a scaredy cat to anything. Rose and Lily have seen each other through the glass door with little to no reaction. I know that's not the same as in person. I am definitely waiting until the kittens are gone, and will use a leash. Crossing my fingers they warm up quick.