I'm home now (with a dog on my front porch
). Aussie Shepheards are FANTASTIC dogs (I'm not as familiar with the Kelpie). When you first introduce them, keep the dog on a leash in the house and hold on so you can control the dog if you need to. Expect a lot of hissing from the cat camp. But, cat's do pretty well adjusting and/or taking care of themselves. Dexter lived with an Aussie Shepheard for a while and they were total buddies. I was sitting 2 mini Aus. Shep. pups for the first year of their life and they moved into a household with 2 cats. They adjusted just fine. They also ate poop and one had the sympathetic pee reaction. To solve the poop proble, they got a covered cat box with a door and placed it with the door towards the wall so the dogs couldn't manouever into it, but the cats could. As far as the sympathetic pee thing, only one puppy did it and he grew out of it. AS's aren't known for having that trait for long (spainiels are another story). I think once he gets settled and comfortable he will grow out of it.
It actually sounds like a good match. AS is a great breed with the only downside being heart defects that effect them when they are older. Not all AS's have it, but it does run in the breed and can shorten their life. But, any breed has some sort of issue or another.