How much anti-freeze?

Ours is an 18x36 24K gallon vinyl in-ground. We have 2 skimmers, 2 returns, one plugged-up main drain, a wall vacuum line and a Hayward light/niche.

How much anti-freeze should I use for each line and should I put any in the main drain line as well? It has a winter plug on it from last fall (diver installed). We haven't removed the plug or used it this year till we figure out if its worth getting fixed.

I always store my underwater light on the deck under the diving board. Is this what everyone else does too?