If you're going to be gone so much of the day, your priority in adopting a dog should be finding a dog who would be content with your lifestyle. You may not be able to get the specific breed you want, and you need to be more open minded about age. Even though you are willing to/want to go on long walks and take training seriously, it's difficult to make up for a whole day of being gone.
That said, there are plenty of dogs who can both be active and would be happy with your schedule. I had an older bichon, traditionally thought of as an indoor lap dog, who was perfect for me when I was single and gone during the day from about 8-5. We would go on a 2/2.5 mile hike in the morning (he was 9 years old at the time, and yes, he loved this- most dogs are more active than people and they don't limit themselves the way we do), and then, according to my housemates, he would be passed out on the couch until about 20 minutes before I got home, at which point we would go on a longer hike (4-5 miles). Currently, I have a dog we rescued at about 3 years old. Due to medical issues, she's very mellow, although definitely more energetic than we first thought. Luckily, my husband and I share the responsibility of taking care of her, so it's easier to stagger our work scheduled so she's not alone as long. We also employ an occasional dog walker and have a kind neighbor who also helps out.
I highly suggest you stay open minded and make your #1 priority in selecting a dog that the dog would be happy with your lifestyle. You really ought to let go of your breed and age preferences. There are lots of older dogs who not only need homes, but are often easier to have for working people. Our current dog was completely housebroken when we got her, and only had one accident ever (she was post-op, very heavily medicated, so I don't blame her). No need to take vacation time to train the puppy or anything like that. I've had dogs all my life. With each of my dogs, our best years together were 8-13/14ish (they've all lived to 15+, with good health until the last couple months). I do sometimes wish I knew what my dog looked like as a puppy, but that's mostly a curiosity issue. I don't think I would love her any more if I knew her longer, or if I had total control over her upbringing. I promise that once you get a dog, it will be a unique family member, and you won't think as much about things like breed, age, or where they came from.