Your shop will be fine, but just on the cool side for Amaryllis. To protect again the bulb rotting, with the cooler temps in your shop, I would cut back on water, wait till the soil is completely dry. The bulb has plenty of moisture inside it. They don't need fertilizer in the winter: You are encouraging the Amaryllis to slow down. In your shop, getting daylight, the plants may or may not go completely dormant. Since mine are outside, I don't have any experience with keeping Amaryllis growing all winter indoors. There are other people on this forum who might have some experience with this. In March or April, as the day length increases, you'll see new growth. Then you can start watering again. Its personal preference as to repotting it. They prefer to be a bit potbound. The other reason for reducing water is to cut down on the nuisance of fungus gnats. They eat the fungus in the wet soil:dryer the soil, the less fungus and the less gnats. They can be really annoying in a closed area.
