Update: After a few days of cleaning, sorting, and calling people about stuff, two trips to goodwill, and more trash bags than I care to think about, I finally have a sewing space! There are a couple of things I can do to make it prettier, because it still feels like a storage room and trying to be creative in that much clutter will be hard.
The space is approximately 8 feet by 12 feet, with the window and door at opposite ends of the long side. I have unlimited access to one plug, and I can get access to another one with a short extension cord. As expected, I don't have any vertical storage space, unless I can rig something up by zip tying pegboard to the front of one of the shelves. I did clear out enough to have two shelves on wire racks for storage, a skinny but tall bookcase, and a couple of plastic drawers with shelves. I have a light and my sewing machine for furniture...my next step is a table and an adjustable desk chair!