I wouldn't bother double digging everywhere in the first year, you'll never get anything planted. In fact many people never double dig, or rotovate. I've only done it on a few troublesome pieces of my plot.
This first year just divide the plot up into bed areas. Then lift the top layer of these and leave this in a heap to rot down - cover it with thick black plastic to stop it regrowing and seeding everywhere. (By next year you will be able to dig it out onto the beds removing any roots you see, as you go.)
Dig out any deep rooting weeds as you go (bin bag for them) bash any big clods of earth with fork or spade to break them up a bit. Rake any lumps to one side and then start planting stuff
If it's still very cloddy and you want to sow seeds, make a drill (a groove an inch or so deep), fill with fine soil or bought compost, and sow into that. You just have to keep the drill damp if the weather turns dry - we should be so lucky
Next year you will be able to turn the pile of now dead grass you lifted, onto the beds removing any roots you see, as you go.
The ground does get less cloddy each year as you work it, and add your plot-made compost or manure if you can get some from a safe source.
Good Luck!
