My sewing room is a separate building from my house and I have a window air conditioner and I use an oil filled heater that you can find at Wal-Mart or Lowes. I only turn my air or heat on when I am plan on being in my sewing room, Honestly I have had this setup for years (probably 10 years)and no problem with my machines or fabric, I'm in Kentucky and we have some cold winters and a lot of humidity in the summer.
the condensation is never been a problem, Like in the winter I will turn my heater on a couple of hours before I aim to sew and everything in the room heats up together now If I took a cold machine into a warm room then you have condensation.
I have a Juki and several Brother machine and I have pretty good stash of fabric and absolutely no problem. Good Luck!