Yes that is normal. Those are the bottom leaves. As the banana plant gets more leaves, the lower ones will start to turn yellowish then brown. Once a leaf is totally brown with no traces of green left on it, cut off the dead leaf. If all the leaves were doing that, I'd be a little concerned. No, you do not need a space heater for the banana. (Bananas are essentially large herbs and are not classified as trees)

The banana will eventually fruit, but the problem is that it will rapidly outgrow that pot before fruiting. I had a dwarf orinoco fruit for me, but it was in the ground and was a good 6-7 feet tall when it did. Maybe someone else here has had dwarf orinoco fruit in a pot and could tell you how large it was when it did.

Misting is ok and would not hurt, but bananas like humid weather in the summer. Due to the dry office conditions in the winter, misting wouldn't help out that much, but as I said, it wouldn't hurt at all. Mist away.