Pregnant Rottie, anything I should know?

so .. my Rottie is preggers, and nobody seems to be sure about anything with her! Her last day of heat was in the 3rd week of August, so I figure she's due around Halloween. The vet who did the ultrasound says the pup he saw looks so small, he thinks they're due the 2nd or 3rd week of Nov.
The vet only saw the one pup on the ultrasound, and Kia's not very big. when we try to mush around her belly to try to get an approximate count, we can only feel one pup! what is up with that???
We've got a cardboard oven box for her, nice and roomy. waterproof mattress pad on the bottom, some blankets on top. she seems to like it, so hopefully she'll birth in there, and not on my bed or the couch! she's on BilJac puppy food now. we've got a babysitter for the other dog, who's just terribly nosy .. he's a mini-schnauzer/wire-hair terrier mix, and while he and Kia get along wonderfully, I just think that he can vamoose for the first few days, to give Kia time to get settled.
We've noticed some leakage from her teats lately, but it's sporadic ... one of the vet assistants said that Kia might be "getting ready to go", but ...

any thoughts? anything I should be sure to do, or not do? what do I *need* to know?

thanks in advance!

~RedMolly