Hi, Logan,
Never use a heat rock or other heating device on or in your cage. Your gliders can generate their own heat. Like everyone above said, what's comfortable for you should be okay. I like my house cool- 68+70 degrees all year, so they have adjusted-lol. And a space heater is good, just make sure they can't escape and don't place near their cage!
As for humidifiers, heat and central air can dry the air and contribute to "fur cracking". I just ordered a Rainbo Rainmate air purifier/humidifier. The mist is very, very fine. Mine also lights up so it will take the place of a night light in my living room for my girls. They bark a lot if in total blackness- after all in the wild there is the moon and stars, right? You can add scents to it, but I will just use it plain. My vet has one in his HUGE waiting room, and the whole place just smells like fresh, clean air. You can get one for a good price on Ebay. I crushed my nose and cheek in a car accident, so this will benefit my breathing, too. Also, at holiday time, your christmas tree(if you do Christmas) will love the humidifier!Sorry for the long post- hope I've helped!
Wendy