We got our pointer x spaniel dog nearly 13 years ago and, sadly, he recently became very ill and we had to make the awful decision to have him put to sleep.
He was really such a lovely dog and a wonderful companion. I miss him enormously. Having a dog also ensures that, as a responsible owner, you have regular exercise when you take your dog for walks - and you get to chat with other dog owners too.
There are quite a few things to consider:
If you are considering going part time, would you have to leave your dog for several hours on its own? We are retired so that wasn't an issue. In any event, our dog was quite happy to be left on his own for a few hours - he just went to sleep - but some dogs are unhappy being left alone and may bark or be destructive.
It is quite expensive to have a dog - you will need a good bed, dishes, food (for a medium to large size dog that can be quite an expense), annual vaccines, flea and worm treatment, insurance (there comes a point, with an older dog, when insurance becomes ridiculously expensive), and possibly kennel, dog walking or dog-sitting fees.
There are several hotels and B&Bs to which you can take a dog. They usually specify that you should not leave the dog in the hotel/accommodation when you go out. We nearly always took our dog and it didn't present any problems - but it does limit your choices to some extent.
With some dog breeds, you will have to vacuum more often and even with dogs that don't shed their coats more cleaning is required.
If you want to have your dog neutered, I believe that now costs around £200.
Another poster made the very good point that as you have children, this would limit the places that you can go to with a dog - beaches in mid to high season (or - if you are lucky - only certain areas reserved for dogs), theme parks, etc., and many pubs and most restaurants (unless you sit outside).
You would need to research which dogs would be most suitable for your family. Some breeds are more nervous and sensitive than others and certain breeds are more suitable for families. I believe collies can be quite lively and their needs are better met in a more rural setting.
As others have said, having a dog does limit your spontaneity to some extent. But for both of us it was well worth that inconvenience. I miss our dog so much (though that is something else to bear in mind - medium to large size dogs live on average 12-14 years and it is very sad to see them grow old and get ill.)