I've been thinking about where I would do my developing, it seems like the bathroom would be easiest, just need to cover the window and seal up the gaps at the door.
A bathroom is not as well-suited as you think. The main thing that a bathroom has that some other room might not have is a drain.
You will need a small work table at the very least, so if your bathroom countertop has some extra space, then maybe it will work. Don't even bother trying to make your bathroom dark. 1.) You cannot get it dark enough and 2.) you must open film canisters in complete darkness. So use a changing bag instead of trying to make the whole room dark.
It is a rare bathroom indeed that is actually large enough and with enough counter space to function as a decent darkroom. Besides; if you live with someone, I can guarantee there will be strife.
If you don't mind carrying liquids back and forth, you can set up a darkroom (for making prints) just about anywhere. I once had a darkroom in a walk-in closet with no running water or drain. I just carried the jugs and trays to the bathroom or kitchen as opportunity arose.
For film, you load it in complete darkness, both B&W and color. Load it into the developing tank, and when the lid is on securely, then you no longer need darkness.
For printing B&W prints on paper, you open and handle the paper in your darkroom that is lighted with a safelight. The enlarger exposes the paper with a white light, but just for the prescribed time only. You develop paper prints in trays on the table/countertop. You will need shelves and work space more than anything else.
For color printing, you need darkness to handle the color print paper, and the trays must be kept at a constant temperature, so having a long shallow sink will let you place the trays in a water bath to hold the proper temperature.
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