I think a lot depends on the personality and breed of the dog, but also age, size and training, and, for a rescue dog, their previous history.
We do at least 2 walks a day, minimum 1 hour total, but usually closer to 2 hours (quite a big dog).
In our area there was quite a big choice of training classes in daytime, evening and weekends, but I think this would depend on where you live. You can also move on to things like agility and advanced training classes after the basics.
If you are going to want to leave your dog alone in the house check out the different breed characteristics as some breeds get more stressed without company, which can be awful for the dog but also might mean destructive behaviour or lots of antisocial barking.
The main lifestyle changes for me have been:
More exercise and reason to walk even in bad weather which I really love, though I know it can feel like a chore.
I can choose to walk in places where I know I will get to chat to other dog owners if I want company or I can choose a solitary walk. I know lots of dog owners who enjoy the social aspect of going to the same park every day for a chat with other owners.
Going out is more difficult as restaurants, shops, cinemas, museums, evening classes or whatever you enjoy doing probably don't allow dogs, so you either need a dog minder (which can be expensive), find places you can take the dog, or build up the time your dog is able to be left alone, though I wouldn't leave my dog for longer than 5 hours. On the other hand, you might find all kinds of dog-friendly places and things to do which will enhance your lifestyle.
I have a non-shedding dog and am not particularly tidy, but I think other dog owners might say there was a big increase in cleaning.
Dogs can be expensive - food, insurance, vets bills, etc, which might be an issue for you.
Overall, for me anyway there definitely more pros than cons - lovely having the companionship of a dog :)