Everybody is giving great ideas. I'll just make a small suggestion. I just built a home and I was fortunate enough to have a counter top installed in my darkroom for the workspace. If I had it to do over again, I would have made it lower. For me a standard kitchen counter is too high. Since you are in the planning stages, I would consider going no more then slightly above waist high. That way, you can look down on the image and get a great view. Plus, you can reach up easier to raise and lower your enlarger. In fact, I would do some measurements using your own body and make sure it is custom made for you. I have a stool in my darkroom. However, I don't use it and I am going to take it out to reduce the clutter. Standing at a properly built table to me is better then sitting.