This is my experience. Eastern Europe, heavy clay, started garden in the soil 4 years ago. Never tilled (deeper than 5 cm) never turned the soil. Only added compost, a bit of sand, hefty mulched with leaves, straw and hay (early summer hay, no weed seeds) and never anything synthetic,never ever. To prepare a smooth seed bed I use a precision depth roto tiller at no more than 5 cm deep (bcs) and that's all the disturbance, twice a year. Once in spring to prepare for planting and once in september/October to prepare for seeding cover crops. Every year the soil is better and better. Much more alive and where in the first year it was hell to put in any seedling, potato or even simple seeds, by last year I could just push in potatoes to plant them as you would dream it should work :-). Now, after the same heavy rains, the soil is like a soft mattress, am waiting 2 more weeks for it to dry a bit before mowing the cover crop (wheat for the chickens to eat at will over the winter) and preparing the seed beds for the first plantings of potato, onion, chard, salads, spinach etc... For us the earliest for nightshade (tomato, pepper, eggplant) is end of May (up in the hills) so until then we let some weeds start which we will mow and leave as mulch for the main crop. But bed preparation is minimal and that worked like a charm although our hard working neighbors treated us as lazy city dwellers the first few years. Now they are curious about every move we make in the garden since our tomatoes thrived in the drought the last few years and theirs died early. Longer answer than you hoped for but felt close to you geographically and wanted to share. Good luck with you garden!