So many Questions! I am new to this web discussion lark, but not entirely new to Allotment gardening.
John 14 did you get any advice? Its tricky, but you could try to scrape a little bark off one of the branches (just a little bit) if it's green then its alive and new leves etc should appear in spring. Try liquid seaweed feed (in sping) this can stimulate stronger more drought resitant growth. If you ever plant another tree I cant recomend RootGrow or any equivalent highly enough. This gives a symbiotic fungal growth which acts like a secondary root sytem which helps trees and shubs take up water & nutrients. It's quite new to home gardeners & not cheap but well worth it.
Chelle 2 Another difficult one. By now you may know the answer, if the green manure did not smother the weeds then I would cover the area with Black plastic or membrane now & leave it all winter. In spring when you uncover there should be no top growth. Dig out all perennial weeds you can but be prepared for re-growth, it will take time but it will work. A rotovator would just chop up the roots & spread them & unless you can keep rotovating as soon as they re-appear. Potatoes traditionally help clear ground as you cultivate at least 4 times in season, (dig to prepare, dig to plant, earth up, Dig to harvest). There are other methods such as cover with cardboard, mulch with very thick layer of compost & grow into that (by implication you need a lot of compost). Try some of each! Good luck.