DARKEYES:

Yes. It's very unfair to leave a very active and sensitive dog alone all day. If you choose to leave the dog in the yard alone, it may bark and start a dog chorus. It may also attract dog-teasing and abusing children. And the neighbors may complain. Besides, doggie is lonely!
ESTHERS VIRTUE:

I have loved so many dogs. I couldn't give all of them the exact type of love they needed, however. So I have learned to be more careful, both for the sake of the dog, and for the sake of my heart.
I've had a BEAGLE, which was a darling dog, and which couldn't tolerate being alone all day, even with a very nice yard. She would run in circles and her bugle could be heard a block away. That was not what the neighbors wanted to hear. We eventually sent her to live on a farm.
I've had TERRIERS, and I am inordinately fond of them. I am a pushover for a dog that will jump into my arms. Some of them, however (the Jack Russell, for example) are much too high strung, much too people-oriented to be left alone all day. I've had a medium-size border terrier, which was very sweet and intelligent --- and enjoyed playing ball alone. Or maybe he was just trying to entice me to throw the ball to him? I think he did all right because I had other dogs to keep him company. However, I don't think he would have been happy all alone.
I've had a SHEPHERD --- very intelligent, and very protective. Of course, they require a lot of care and brushing and cleanup. And they are also inclined toward hip dysplasia. Mine was a hobo. We got him that way, and we lost him that way.
That said, there are some SMALL DOGS that can adapt to being alone all day. If a doggie door works for you, and if your yard is actually secure, and if there are enough dog toys in the house and yard to keep your buddy amused, it can be done.
I would get the dog while you are at home on vacation. That way you can establish potty boundaries and watch the dog's reactions to your environment. And you can introduce lots of toys, helping the dog choose them instead of chewing on your furniture, etc. And it will give you a chance to crate-train the dog.
I think dog crates, if large enough, are wonderful. I taught my schipperke dog to love hers. It was her home, with her toys all inside. She would go in there in preference to anywhere else in the house, because she felt "safe" in her own little den. My dog was so protective of her home territory, and of me, that I would need to fasten her crate door if I had a visitor. She was the greatest watch dog in the world. She had more courage than judgment, however, and would have attacked an elephant to protect me. She was a SCHIPPERKE, about 20 lbs, all heart, as fun as a dog can be. Unfortunately, she probably shed more coat than any other dog I've known. But she was wonderfully waterproof and required no haircuts. And all her life she had not a single health problem, until the sudden liver cancer that took her at age 13.
There are more places to get a dog than the "pound." There are SPECIAL RESCUE ORGANIZATIONS for almost every type of pedigreed dog. You might want to contact and visit some of them. I'm not saying that mutts are not wonderful. What I AM saying, however, is that after losing my beautiful GREYHOUND MIX to some type of disease she caught in the pound, I shall not be getting a dog from the pound again. For me it was heartbreaking. She was the best buddy ever to my schipperke. And she was so sweet, laying her head on my knees, looking up at me with obviously adoring eyes. She knew all the house rules when she came home with me. She was a perfect dog already. And I shall never forget her.
Especially if you work, I would choose a MATURE DOG rather than a puppy. Some dogs are quite destructive, especially if left alone for long periods of time, in their puppyhood. And my schipperke was a bigtime chewing machine until about age 2. If you think about it, 2 years is a long time, extremely slow because of the owner working full-time. So crate training was vital for her. Then one morning she woke up, decided that she knew all the rules and would even enforce them, and was the most proper dog you can imagine. Anyway, how can one train a puppy when one is away at work all day?
When I was very young, my grandmother told me that a RAT TERRIER was the best dog in the world. Truly, they will keep your home free of vermin of any type. And they are also a barrel of fun, extremely intelligent, and eager to learn. I used to think that she meant a wire-haired fox terrier, but that wasn't so. Seems I have heard that the rat terrier is actually a breed. Probably better have a fence they can't burrow under, because I think all terriers like to dig.
Yes, the SIZE OF THE DOG can matter. Those who work and are very tired on the weekend, and those who have any physical disability or use a wheelchair, will find a dog this size very easy to bathe, to pick up, to carry in a large shoulder bag in the case of disaster (well, if there is broken glass or gasoline on the ground, the dog will need protection). Perhaps you have none of these problems, Esther'sVirtue. However, if you ever need a dogsitting person, the elderly and physically disabled can probably manage a dog this size quite well, using the kitchen sink for bathing the dog if necessary, and drying it in a towel right in one's lap. Yes, it pays to look ahead and weigh these factors when you are choosing your doggie life companion.
Finally, I want to wish you a lot of wonder and joy in your journey toward that very special canine friend who is waiting and hoping for just you, because noone else will do.
Adieu