I have a 40 foot High Cube shipping container on my property that has my shop in 15 feet of one end and storage in the rest. Ventilation is critical. I cut a small opening in the end of the container and used 2x6's to frame it out. It has small windows on each side and a fan like this in the middle.
iLiving 12-Inch Wall Mounted Exhaust Fan with Variable Speed, 960 CFM, 1400 SQF Coverage Area, Silver
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I built a frame that can tilt and put four 100 watt solar panels on the roof that charge four 6 volt golf cart batteries and powers everything I need in the container. I have two security cameras on the container, a weather station, and lights. I have a small mill and bench lathe and the only time I can't use them is in the winter when the temp gets below 20F.
There are a lot of ways to do it. If you cut holes in the walls you have to reinforce the wall since the shipping containers are designed to put all the load to the corners, then be stacked like blocks.
If you insulate, you need to use something like a closed cell spray foam or you will fight mold. Insulation like the pink fiberglass stuff or anything "loose" will draw moisture as the steel walls still condense moisture unless the surface is closed with a bond that cannot let humid air get to it at all.
For storage I built shelves on one side and install 24" deep pallet racking style shelves on the other side with a 48" aisle down the middle. You can also drill through the walls and bolt on boards like 2x6's to attach hooks or do a french cleat system.