No reason to close Facebook. It's at the top of the list most likely because you used Facebook more than the others during the 24 hour period. There's no reason to worry about battery. Just enjoy your device.
I force close certain apps when I want them to open at their main/home screen or in cases where they might be exhibiting odd behavior. Back in my legacy BlackBerry days I’d kill everything off when done using it, and Android needed clearing at times.