I think the answer to grass is to turn it under upsidedown, making sure there is no green showing and plant large crops because they are easier to hoe around. Courgette, potato, broad beans etc and then every time you see even a hint of grass showing above the ground hoe its head off. In the end the grass gives up, though couch can take quite a long time.
I took over a very weedy patch Feb last year and one piece had been a path so the ground was not only covered in course grass but the soil was solid. I cut off the grass just below ground level and then hoed it. Then continued hoeing twice a week for about 2 months. Part were potatoes and the rest I sowed dwarf beans as a ground cover. There is no sign of the grass now.
Potatoes and courgettes in particular seem to clean up soil, they seem to deter the weeds.