I'm a place to land, but not be constrained.
I'm always there to cheer you on, but then I can't eat.
I'm one who uses a modem, but then can't even list files.
I can hold volumes, but I keep away from ladies' fingers.
When all else fails I decide, but only when the night air is silent.
And if you see me from behind, you'll know I'm fit to be a king.
What's this all about?
Each line should be solved independently, and the answers to each line are related. The title tells you how to solve each line except the last one, which involves a different type of wordplay.
I'm a Japanese religion, but don't care about the initial SE site's initials.