The Whippet is an excellent choice for your work schedule but I do worry about puppies that are left alone for most of the day. They have a lot more energy than older dogs and tend to develop bad habits (like digging, barking, etc). It sounds like you have already figured out the housetraining, and of course coming home in the middle of the day is a big help, but the problem is those hours you are away.
Would you be able to take your puppy to a doggy daycare for the first several months you own him? Letting him interact with other dogs and run around more is a much better option. If you cannot, I recommend an older dog. If you really have your heart set on a puppy, just be aware that there may be problems down the road.
In addition to taking him for the evening walk, you should also get him involved in puppy socialization and obedience classes right away.