I took over a new allotment, plot 248, last August and it was covered in couch grass, bindweed and lots else besides.
I have more photos and a blog about my progress here. I decided to play the long game and try to rid the plot of most weeds by covering with old plastic sheets and mypex in an attempt to starve the weeds of light. As soon as possible I added manure under the covers to get the worms doing the digging for me. Nine months later the only weed of any note is bindweed and I am forking this out one bed at a time but I will leave some of the worst patches until I can be sure that I can maintain what has been cleared. I was fortunate in having Plot 248 as a second plot so was not in a rush to plant up, particularly as it was getting late in the season.
I think it is best to be realistic and conservative about what you can weed thoroughly AND maintain for this season’s crops and, for the rest, let a combination of light excluding material and organic matter do the weedkilling and digging for you. This will give you a great start for next season. You can always add to you cultivated area one bed at a time as your back defeats the couch.
I think Bluebell’s comment, “break it down to bite size chunks” is great advice.
Bonne chance!