Jessika answered your questions nicely! I just wanted to add some info about the plastic/silk plants.
Silk plants are good for fish that have fancy fins (bettas, angel fish etc...) as they are a lot softer & smoother than plastic plants & won't rip any fins like plastic plants can do. But if you just have smaller finned fish plastic is fine, it's cheaper too.

I wouldn't cover the heater, you shouldn't have the water above 70-78 so they should be safe. If your heater does heat up to the point where it burns your fish it is time for a new heater.