You may have addressed several of these issues, but from my own experience building one in the garage I remember these coming up:
Ventilation - This is not a luxury. This is a requirement. Does this have a 'roof' on it? When you shut the door, is there a way for the air pressure to get out?
Heat & A/C - Will make it much more enjoyable.
Fire extinguishers - 2. Yes 2. One on one end, another on the other. In that small space they can be the very small type, with a larger unit outside the box.
No Smoking signs - Should be clearly posted whether you allow smoking or not. I have had friends, stranagers, workers - whatever over to my house and they don't think twice about walking around with a cigarette lit until they see the signs.
Power outlets - you cannot have too many. Extention cords are messy and easily overloaded and are a tripping and fire hazard.
Lights - You can never have too much light and as you age there never seems to be enough. If you think it is enough, add 50%, including overhead shop lights and moveable spot lights. The hidden spots look sweet, but they don't provide the maximum amount of light from multiple angles that is so helpful when looking at tiny detail. Can you get outside light in?
Magnification - I have a lighted magnifier on my bench. Wouldn't know what to do without it.
Tumbler - keep it outside that room, somewhere else in the basement. They are dusty and noisy - 2 things you don't need in there. Think clean!
Rubber floor mat - You will be on your feet more than you think. Take care of your joints.
Cleaning - keep a dustpan and small handheld brush for quick/easy sweep ups. I use it all the time rather than try to do one 'big' clean up later. In fact I bought 3 small paint brushes to use on the machines.
Organization - sit in there before you start and go through the motions... where do you want to have your bullets, your brass, your powder, your other stuff. Get organized FIRST and you won't have to redo something later. Ask me how I know.
. SEEriously consider putting up some pegboard. I wish I had a pic of mine after all the stuff was hung. You will not believe how many tools, die heads, and even small shelves for books you can hang on the walls.
Cabinets - You are obviously handy, so think of what will you use the upper cabinets for. Many items can be mounted on pull out shelves so you don't have to take it out, unpack it, place it on the bench, yadda yadda... for instance RCBS brass multi machine, brass trimmer, electronic scale. Pull them out, use it, push it back. HUGE time saver. That way the power outlets can be inside the cabinets as well. Have a pull out on the bottom shelf of each one and stored items above it.
Storage - Powder and primers should be stored separately from each other and kept udner lock and key. No question about it. All liquids - cleaning, oils, etc, etc should be kept in one location too.
Television - FWIW I would never have a television around while I am reloading. I find I even turn my radio off. I want 100% concentration.
I'm sure there's more but that's all I can think of off the top of my head.