Ours are heated and secure, limited access for only customers. Outdoors storage units are exposed to elements when loading & unloading, cold, much more probability of mice and rodents.

Many factors come in to play; how long do you need to store your belongings, do you need access regularly, (Murphy's law what you need will be in the back). But in general a 10x10 unit can accommodate 2-3 rooms of furniture, 10x20 unit can accommodate 4-5 rooms.

No.

At least 36" on smaller units. All large units are 78" wide.

Standard unit sizes are 5x5, 5x10, 10x10, 10x15, 10x20. As this was a retrofit of a building many different sizes in between.