Patti, your temperature is far warmer than what all my orchids get in the fall/winter months. My two greenhouses are kept at 65F, but when it dips into the mid-teens, they often will dip closer to 60F. The house thermostats are kept at 67F during the cold months (night) but the house will be warmer than that during the day.
Regardless of where you keep your orchids, they will certainly do best with bright, indirect light. High humidity is nice, but to me at least, bright light is more important. Your planned mix should be just fine. Keep in mind, some of the orchid roots will die, particularly when they are in a dormant cycle. That's perfectly normal. Some of my epiphytic varieties lose all their roots and a few will lose most/all of their leaves during dormancy. Thus, "rotted" roots are not necessarily caused by over-watering or water-retentive media. Check those roots when you re-pot.
Good luck.
