Start simple. Put in a strong bench/table that runs the full length of the space. Mount a couple of vices on the table. Run a multi-drop power strip to the table. Put a 1x30 belt sander on it. Put a bench grinder on it. Get a portable variable speed bandsaw, mount it vertically and pit it on the bench. Put a small drill press on it. Get a flexible shaft Dremel and put it nearby. Install a tool cabinet underneath it. Fill the cabinet with clamps, drill bits and diamond burrs (the burrs are for the Dremel). Put something on the wall that allows you to put your files in individual pockets or slots, and arrange them so that you can easily find the kind you need (sort by type and cutting depth). Put in numerous light sources... different types.... fluorescent, halogen, incandescent and natural. Make sure you have adequate ventilation.
Under the bench put another cabinet that contains supplies... sandpaper, handle materials, billets (all marked as to type).
Build a shelf on one of the short walls to hold safety equipment (respirator, hearing protection, gloves, goggles/safety glasses). On the other short wall build some shallow shelves with lips to hold chemicals... Ferric Chloride, Acetone, Denatured Alcohol, Tung Oil, and so forth. Better yet, put in a shallow Rubbermaid cabinet to hold them, so they won't be exposed to sparks.
Outside, get a barrel that catches rainwater that you can use for keeping your metal cool while grinding.
Put a sign on the door that says "Enter At Your Own Risk".