tips for adding a dog to the family?

We're finally living in a place where we can accommodate giving a dog a
nice home, something my dh and I have wanted to do for a long time. We
recently moved into our first home, have more indoor living space than
we've had before, and more yard than we can even being to figure out how
to use. We're backed by woods, and have a woods/park at the end of the
street as well as a playground/ballfield down the street, a quiet
neighborhood, and plenty nearby to walk to. We've fenced the portion of
the back yard nearest the house.

We have a ds 6.5 and a ds 2.5, and a male cat 4.5. Dh grew up in a home
with dogs, cats, etc. the kind of place where anyone who turned up on
the doorstep was welcomed to find a comfy place to sleep. I grew up with
lots of rescue/hand-me-down cats and later in life came to know some
dogs quite well whom I enjoyed very much.

I've been searching rescue sites for a dog; we've decided on a border
collie mix, as I really like how smart they are. I've found a 7yo male
needing a home because of a divorce situation. He's been for one visit
with his owner with me and our 2.5yo ds, and their interaction and
energy together was very good. He didn't chase the cat, who hissed and
puffed up and then I put him in the bedroom. They're coming again
tomorrow to meet the whole family this time.

Whether or not we are ultimately a match for this dog, I'd appreciate
any tips on bringing a dog into our family, in relation to the kids, the
cat, and me, who will the primary caregiver of this dog. I just bought
the Cesar Millan book, and have ordered a couple of cat tree things to
give the cat some perches in the public areas of the house so he doesn't
feel like he has to hide all the time. Ds 6.5yo's room is gated off from
the toddler, and it is a place the cat can get in but a dog wouldn't be
able to. I am also planning to make a similar situation with the laundry
room.

What else can I do to make a successful transition for all?