Newbie here, basic questions

So I litteraly saved this printer from the dumpster. To my surprise, it seems to work just fine -- I just finished printing the benchy.

I have some questions though, as this is my first 3D printer:

1. What is the right procedure to switch the printer off? Do I just wait until it's done, let it cool down and flip the hardware switch to off?
2. Loading the filament -- I heated up the printer head, threaded it in past the wheel and then used the load functionality, increasing the step by 100mm. This took ages and I didn't know how to stop the loading once filament started coming out. Is the proper way to do it by hand as far as it goes and then do the last bit slowly, 10mm at a time?
3. Fans. There are two settings for fans in the menu, one turns on what seems to be additional fan next to the printer head, the other one vents the box. When do I use these? Are they for cooling down?
4. LED lights -- same story as fans, can this be turned on only while not printing? It'd be nice to have the lights while printing is ongoing. But not a big deal.
5. Calibration -- my first layer didn't stick properly. I did notice when calibrating the bed that the middle seems to be lower than the corners. I guess I need to raise the bed a little, especially since I'm printing small things that start in the middle?

Thank you in advance for helping me out!