If you're going to have a personal factory, you're going to need to make it enjoyable to work in.
- Furniture: make your own, sized to your body and oriented to your working preference (sitting vs. standing, etc.)
- Paint: all my containers are coated with white, high-reflectivity roof coating to keep them from getting too hot in the sun. Having just painted the inside of Shop-In-A-Box #002, I highly recommend it: it feels way bigger than it did with the gray original. Also, this paint is supposedly more resistant to mold than the original coating (we had some serious growth after leaving the container sealed with the lights on and water from the water table evaporating for several weeks)
- Floor: standard containers have some wacky plywood treated to make it insect-, flame-, and rot-resistant. It's really nasty to get a splinter from; if you care, I recommend floor tiles or a garage paint (may or may not work on wood; lemme know your results if try it)
- Airflow: get big fans, and get more than one. Plasma cutting and most other processes that are any fun produce nasty fumes. Circulate clean air in from the outside and push the dirty out. This is as if not more relevant to safety than comfort. Here's a useful EPA document on air quality (pdf); go well above their recommended CFMs per square foot, and keep in mind that a fan's CFM rating is going to be far higher than the actual amount fresh air it delivers in real-world conditins
- Roof: the ladder mounted on the interior of my door is the most useful thing I have ever made:)
- Cord management: I have extension cords with outlets every several feet run inside along the ceiling's edge
- Orientation: this matters for solar gain and prevailing wind if you're outside. Whether inside or outside, think about the positioning of your container's entrance relative to other tools and/or workspaces that you'll access. If you're going to repeatedly use a press brake
- Climate: toughness combined with attention to the above will be enough for most people. If you're getting hot in the container, get more fans: more airflow is going to improve your air quality, and the only downside is that you'll scatter papers. I don't like living in cold locations, so I haven't had to deal with a heating system. When I do, it'll most likely be a small, DIY wood stove surrounded by some rammed earth for thermal mass and located near the middle of the container.