Storage! For years I've recommended new guys build three times as much storage as they think they might need, and to understand that eventually even that won't be enough!
My best storage areas are "book shelves", made no more than 8" deep but as wide and tall as I have space for. Wider shelves allow me to loose small stuff too easily! (And I like to paint my shelves white, to help me find small items that might otherwise get lost.) It is important to anchor such shelf units to a wall to prevent tipping. Those shelves I want to protect from dust get simple 1/2" plywood doors hinged from the up-rights.
I find that long plywood shelf boards are prone to sag so I only use 3/4" solid boards, usually (so called) 1x8 pine (actually 3/4" x 7 1/2"), and no more than two feet wide per unit to prevent sagging under heavy loads of bullets, etc. I attach cheep 1/8" white hardboard or paneling to the rear for lateral stability.
Shorter book shelves can be attached to a wall, say three feet above the floor, to leave the floor clear for boxes of other stuff.
These simple shelves are strong, easy to make and pretty cheap too.
Attaching a case trimmer to a closet wall is ingenious! Good going ---