I have done the same sort of project with some of my plants when the flowering area was overloaded. I grow in natural soil and do not know how it would work if in a coco coir or peat-moss based soil. Hope that my experiences can help you out or give ideas to think about.
Yes, the sunroom or porch will work. The temperatures you mention will help keep the plant in a type of dormant stage. Is the sun-room heated or are you basing the temperatures you mentioned as being what you notice on a thermometer now or have you checked your overnight lows during the last several winters? The plant will tolerate colder temps every now and then but dropping to freezing or below for a week might be a problem
To keep the plant healthy yet still in that semi-dormant stage I would not recommend an incandescent bulb. Give the plant a quality light, enough to keep photosynthesis going but with minimal growth. Some growers were able to have good plants all the way through to maturity using the 'curly-Q' compact fluorescent light bulbs. There were grow journals showing how they did that. Those would be a better option than incandescent. But either type of bulb is going to be hard to find, even at a big-box home improvement store since household lighting is going to LED bulbs and fixtures.
I gave my dormant weed plants 14 hours of light with a brief period of light in the middle of the dark period like
@Azimuth brought up. Put the lights on a timer 'cause that beats having to get up in the middle of the night to go out on a chilly porch. Will your neighbors be seeing the light come on and go off every night? Something to think about.
The plant will still need water but not as much nor as often so you will have to figure out a schedule. As mentioned above there is no need to worry to much about providing fertilizer until they are ready to go back into an active growth stage.
I don't put my Marijuana plants into a dormant stage anymore but I have using our backroom to store my outdoor kitchen herbs and flowers over the winter for several years now. Same sort of pluses and minuses except there is a south-facing door-wall and window. Occasionally I turn on a couple of 4 foot florescent lights with grow bulbs. I water those plants every 3 weeks or so until the end of February. Then slowly increase and by mid-March there is new growth on the the Rosemary and the Geraniums will start showing new flower buds. The other kitchen herbs are kept in a stall until mid-April. This winter there are about 30 herb or flower plants back there and hoping to have it organized by Thanksgiving weekend.