Unless you have a heater your greenhouse will only be as warm at night as the ambient air outside, so if its 10F outside it will be 10F in your greenhouse. The only difference is your plants will simply freeze to death, not get frostburn or severe windburn before they die.

You could wander over to the greenhouse forum and post more specific questions about greenhouses and there are lots of helpful people over there, or, you could buy a book like Ortho's "All about greenhouses" from Home Depot and get the same answers.

Zone 5 is going to require a lot of heat to keep any sizeable greenhouse warm enough to grow most "aroids" without them stalling out and going dormant. There are many types of aroids and most require heat at about 50-55F to really stay up and going and hopefully thriving in the winter. You really want to learn what you need to do to do it properly and give it a lot of thought.