I often see a requirement for prospective owners that they have a lot, field etc with a high enough fence. I read somewhere that dogs were time intensive not space intensive.
What other requirements are either recommended or required?

Dogs do need exercise, but I've seen people successfully manage even working breeds in small apartments. They just make sure the dog gets adequate exercise every day by walking them, playing with them, etc. Some breeds like to run, others not so much, and individual dogs of any breed can differ. Most dogs are much more active when they are younger, more sedate as they age.

I often tell people that they should think of dog ownership in the same way they think of having and rasing a child. They need food, water, a warm place to sleep and medical care. They also need to be socialized with lots of dogs and lots of people.

After that, an owner needs to research the breed or mixes of the prospective dog to be sure that it's breeding will fit the owners lifestyle. (EXAMPLE: If you are unable to walk 2-5 miles a day, or throw a ball for 30 minutes several times a day ... you may not want a Border Collie, a Dalmatian, a Pointer, a Lab or a Great Dane).