For boarding though if you have a carry-on it does make sense to board earlier than later especially if your carry-on cannot go in the cargo hold but more importantly because bin space is not guaranteed except maybe in certain cases (like first and business class).
I believe SSSS can also be assigned randomly too as well, as I've had it once but at the time, I only flew maybe once a year and did things normally (booked online, paid with a CC, no issues, etc). So it can also be done randomly to ensure additional security.
For the lightning thing, the way people are generally killed or hurt by lightning is because there is a ground (and standing on the ground is enough). So while in the air, if the plane is designed correctly, lightning strikes will not harm passengers like it would if you got struck while on the ground or standing on something that is touching the ground and where the electricity can get to the ground.