I just got the Raspberry Pi 3 Model B+ and installed OSMC on it. I got it to turn off and now a red light is showing on the Pi itself.
The questions are: How do I turn the Pi on again? and Is it safe to pull the plug out?
At this point yes. Re-plug it to restart. But, except for needing to unplug it to move the device or some other reason, the device is designed to run 24/7. It uses very little power at idle and should cost less than $5/yr.
What’s the best way to put the Pi to idle from OSMC?
Do nothing. Leave it as is. If it’s not playing media, it’s as idle as it gets.