Hello James. I’ve found that it really is vital to have compost/composted manure to spread before you start growing. Even if the underlying soil is fertile the compost gives you a pretty clean surface to plant or sow into. I’ve tried small areas just mulching with silage sheet to kill weeds and then planting in to the (clean looking!) soil. Weed control is almost impossble, especially in wet conditions and grass weeds are difficult to kill by hoeing.
Ask around and you may well find friendly farmers with manure. My experience with local farmers has been really positive and I’ve found them interested in what I’m doing. I’ve been fortunate to meet a local cattle farmer who delevers manure in exchange for vegetables.
If you start small (1/4 acre or so) you won’y need so much manure and can still grow a surprisingly large quantity of veg, then grow as demand for your produce grows.
Black silage sheet is good for killing a large area of grass, but I’d get it on as soon as possible. Spread some manure before putting the sheet on.
All the best! Andy