Posted: 23/09/2014 at 20:48
This is going to be a long job.
How do you eat an elephant....in small chunks.
The area with Knotweed, i would leave for now. Continue to nuke the JKW with glyphosate every time it pokes a new shoot through.
Pick the sunniest area for your veg patch. If it has perennial weeds then give them a dose of glyphosate so you start with a clean sheet. You can do that now. Over the winter fork the area over, removing any rubble and roots as you go. If you can get a load of well rotted Farm Yard Manure, lay that on each bit as you clear it.
In the spring you should then have a good patch you can give a quick fork over to incorporate the FYM,and add a handful of Fish Blood and Bone, and then plant.
For the lawn area, proceed as above without adding Farm Yard manure. Seed or Turf in Spring.
If you spend his winter on thorough soil preparation, it will save you a lot of frustration in the long run.
I would not use membrane except for paths with gravel on top.