Hi Andy
I agree with everything Charles has said and you are right not to underestimate the size of your task, in my experience it is precisely this that brings about the demise of many peoples cultivation aspirations. I think no-dig, if managed well, is the least time consuming way forward but be under no illusions about the amount of work involved. Sermon over; I would think, based on the history of your plot, that the fertility will be quite adequate for most crops, so there is no immediate need to import manure or compost. However; the weeds will need attention and covering an area with black plastic will eventually kill those and and allow you to concentrate on an area that is manageable. I would rake off the top growth, (a good quality rake makes a difference here), and start planting. Of course there will be a lot of regrowth and reseeding to be dealt with but its a case of time management, i.e. don`t bite off more than you can chew.
Hope this advice is helpful Pete