Is it okay to leave iphone 5s ON during the night time?

Will it affect the battery life in a negative way?

I usually charge my phone at night while I sleep, with the phone still turned on. But if it is on like 70-100% battery, there should be no problem not charging it and keeping it on while you sleep.

Yes, remember it is a phone, so you might get an important call at night. If you don't think that you will get an important call then you can turn off the phone. It will definitely save battery life. Make sure you restart your phone once a day to refresh the phone, just like you have to in a computer.

Yes, it is ok
No, it will not affect the battery life

Yes, I haven't shut my iphone off in 2 years. You can also mute it with the corner switch.