Hi Ken and Brereton
I think there are two things that need addressing, these being to clear the plot of weeds and to improve the soil.
Annual weeds soon die off but some perennials take much longer although you say you have twelve months before thinking of cropping and this should be sufficient to clear almost everything if you cover with black polythene or mypex-type membrane.
Why not start the soil improvement immediately by adding as much compost/manure/green waste as you can get hold of before laying the plastic/membrane? The manure needn’t be fully formed compost as you have twelve months for it to mature during which time the soil fauna will be digging the soil for you. The organic layer will also help with weed suppression but you do need a thick layer to combat many perennial weeds unless plastic/membrane is used on top.
I definitely would NOT rotovate. It is the best way to propagate bindweed and other weeds by root cuttings! Let the organic matter do the work.
I would leave sowing the green manure until you have a weed free plot.
This link might be useful although, since doing it again, I have mucked and covered at the same time.