I would look at this as a long term project - it could take 5 years to get the land in good heart. Just off the top of my head thoughts for you
You
must clear the ragwort for starters. There are specific controls for horsetail (see Weed Control -
Horse or Mare's Tail - Equisetum ArvenseThink about growing comfrey - you can start with just a few dozen root cuttings and multiply 20 fold in the second year from root cuttings, see
ComfreyIf you've got any chicken/turkey units locally, you may be able to get hold of masses of used litter which will add fertility and humus. Also any local stables with spare horsemuck - as much as you can get.
Don't just grow veg - think about free-ranging poultry. I'm convinced the sustainable answer lies in mixed units.
Invest in a plough / rotavator attachments for the tractor. 3 acres is a bit beyond a Merry Tiller.
Deep rooting herbal leys or green manures to help break up the clay.
Check the pH and nutrient levels. Acid clays are sticky and adding lime to increase the pH helps them break up.
See
Compost, Fertiliser, Soil Improvers and Improvement and specifically
Garden Lime - the Vital Fertiliser!What's the drainage like?
Unless you're full-time on the plot, break it up into manageable sections.
Pigs are great for breaking new land up - might even make a few bob but you'll have to make sure they're well secured, housed and comply with regulations.
Would you swap for 3 acres of stony hillside in Wales?

Willow biomass could be worth looking into
Wind - only real long-term answer is wind breaks, consider productive hedging - elder, blackthorn, Farleigh damsons, dog rose, hazel, rowan, hawthorn. Some for you, some for wildlife. Fast growing conifers - leylandii - have a bad reputation but they grow very fast and shelter whilst your permanent hedge grows. Then they can be cut down and used as firewood or chipped as mulching material
If you want to grow spuds look at Sarpo Mira as a first one. It's a tough thug. Blight resistant and seems to suffer little from slug and worm. The foliage drowns out weeds and the yield is huge. Drawback is not everyone likes the flavour/texture although we love them for mash and slow cooks like hotpot.
Hope that sparks some approaches for you - good luck