Congrats! Enjoying grandkids myself, all the old Tonka toys and trikes are getting another workout.
Advice? If you aren't already a patient person, learn to be one; first the wife and her changes (you are now #2, and that's the way it is), and then the kid(s) in a real short time when they are mobile little sponges that absorb everything around them even when you think they aren't paying attention or don't understand what is going on. Enjoy the adventure, one of the best life has to offer.