Sarah,
my Grazing Rye didn't get that far, so I can only give you the theory as I understand it. Unless you're going for a no-dig scheme you will need to cut the rye down and dig it into the soil before you can use the bed. I understand this can be a bit difficult with Grazing Rye and that you may need to do it a couple of times, or do it once and cover it for a few weeks. In addition rye can inhibit germination for a while, so you need to do it early -or plant rather than sow. If you start your beans or brassicas in modules then you sgould be fine.
That is why I am planning to grow sweetcorn, I start it in pots and grow it through a membrane mulch, so it should suit quite well.
There's more in the HDRA factsheets, if you're a member.
Jeremy