I have created 5ft wide beds with 2ft paths. They have worked well, but if I had the space, I would have made the beds 6ft wide. I think that being able to step onto the beds is a great benefit of this no-dig system.
I planted 3 bush courgette plants across the bed, but they spread well into the path on each side.
Also I grew Sarpo Mira potatoes which needed lots of space as the tops grew up to six feet in length. We are in North Wales and it seemed to rain every day from St Swithens day onward, so that might explain the rampant growth. They fought off blight, though and gave a good crop.