My biggest regret is that we didn't understand the soil. I'd practiced organic gardening for years, but we were clueless about soil biology and how to nurture it for soil building and fertility. For our first garden, we had a soil test done by the cooperative extension office and added their recommended doses of lime, nitrogen, phosphorous, and potash---all chemical(!)---because we didn't have manure and compost yet. We tilled repeatedly. The same was true of our pastures. Our land grew a lot of blackberry brambles and poison ivy when we first bought it, so we scraped off most of the topsoil and basically put nothing back except clover and orchard grass seed. We plowed for our first quarter-acres corn and wheat crops. Several years ago, we finally started finding resources on regenerative agriculture. We started an entirely new approach, and Dan sold our plow and disc-harrow. Building the soil nature's way takes time, however, so we're just finally starting to see the beginnings of improvement. The areas we repeatedly plowed and tilled are the areas we now struggle with the most!
Related to that is something else we wish we'd understood. We didn't understand the difference between lawns (which we grew up with) and pasture. This was before we had goats, so we were relying on other methods to keep it under "control." Dan bought a riding lawn mower and pretty much scalped the pasture like a lawn. The idea with lawn is to cut it as short as possible, so you don't have to mow again too soon, right? WRONG! The fescue came back, but we killed the vetch and other plants soil needs for plant diversity. Another hard lesson learned.
For the third, I would say Dan and I both wish we had invested earlier in the proper tools and equipment. Money has always been in short supply for us, so we often thought we could save it by doing more by hand. That might have worked if we had a large family or community to help, but five acres for two aging middle-agers is a lot to get going. A couple of examples are our farm tractor and sawmill. About half of our five acres is wooded---mostly aging pines giving way to young hardwoods. It was frustrating to have to go buy lumber at a big box store when we had so much potential lumber right down the hill on our own property. The tractor and the sawmill enabled Dan to drag the fallen pines up to the barnyard and saw them into our own lumber and timbers for building. Our savings in buying building materials has more than paid for these two pieces of equipment.
We've learned that for us, the best approach to tools and equipment is to invest in both low- and high-tech options. Hay, for example. Dan usually harvests it by hand with his scythe, but we also have a sickle mower, which we use if rain or weather is an issue.
I do want to add that we value all of our mistakes and problems because we've learned so much from them. We've learned to call everything either an experiment or a prototype because we know we likely won't get it right the first time. But we know we'll learn what not to do, or at least pick up some valuable experience and information for working toward our goals of self-reliance and sustainability.