Hello Judy
This sounds promising and a really good use for old bales of hay and silage. I would unroll them as soon as possible to give maximum time for starving all the pasture plants of light.
Next spring there may be some couch grass and perhaps some dock or dandelion growing through, they are best dug out, and I would also gather up any mulching material where vegetables such as salads, spinach and carrots are to grow, to keep slug numbers down there. In fact you will have quite a few slugs next year, but they should decrease through the season.
For growing leeks and courgettes, the mulch could be left in place with plants set out through it.