I second the motion on the sink. I made one out of simple plywood as stated and I got a huge sink for relatively little money. Dirt simple to make, too. I addeed a touch where I had a large sheet of plywood ripped and I put a piano hinge on the sink backboard and this piece of wood and it served as a large lid. I could raise it to use as a sink and lower it to use the sink as a large table top for JOBO, etc.
Also, I like to have my enlarger close to the developer tray to minimize the amount of walking to the developer. I might change the arrangement so the enlarger is close to the developer and the print washer or holding tray is near the door.
I don't see a spot for ventilation. Are you putting in a fan?
Do you have to cover a window over? If so, consider insulating any airspace created when you close it off. In the summer, this can really become a hot spot.