My experience with a darkroom in a laundry is that most importantly you need to separate wet and dry work areas. Also, make sure you have enough bench space for your enlarger and photographic paper (mine was on the floor - not good!). I used to air dry my prints in a different room. You will probably end up doing more prints than you think - buy the box of 250 sheets. You should check how dark or not so dark your bathroom really is at night by sitting in there until your eyes adjust. I made a timber panel for the window that just clipped in when I was working in there. You can buy foam draft sealing strips to fix any light leaks at the door. But having said all that, I suggest you start with a basic set up and fine tune it to suit your work processes. Enjoy - I'm envious!