Wow you may as well carry on and write a book!
Interesting though, you have found enough time, energy and materials to do a lot of the necessary graft to clean your soil. It sounds as though you are nearly there and I read recently of someone hoeing marestail for three years and it then disappeared! It may depend if it is growing freely around the edges of your allotment which would mean it spreading back in, however well you cope with it. I have similar issues with bindweed and occasional but diligent weeding with a trowel keeps it muted, but it is still there after many years.
Fair point about heritage seeds, or just use modern but non-hybrid seeds in some cases. Slugs I think should diminish because their numbers are always high on overgrown soil and they take a while to die off. You should not need pellets next year, or perhaps a tiny amount eg twenty in the whole year for the whole plot, just near tender plants at key moments. I have found that ponds, frogs etc are often not hugely effective – I think because of how predators do not eat all their prey. Sometimes I find a toad under spinach leaves, and slugs under leaves nearby…. probably the toad’s larder.
‘Wildlife control’ of pests is often exaggerated and I find the main purpose of companion planting, for example, is my enjoyment of beautiful flowers amongst the vegetables. Good luck with a new season.
PS don’t worry about nutrients leaching out, that happens mainly if you apply synthetic fertiliser at the wrong time or in overdose: organic gardeners agonise unnecessarily about leaching. Bare soil in winter helps to keep slug numbers down! but it is certainly good if you can grow winter vegetables.