Have a look at permaculture for self sustainable agriculture, no need for fertilisers etc.
You'll need probably at least half a hectare to start approach food independence. But even with that you will struggle to get the bulk. Potatoes, Jerusalem artichokes, etc will be your friend there.
Depending where you live you might be able to grow most of your vegetable intake on less land, but you will also need a significant chunk of legumes for protein.
And in terms of fruit, you basically need a decent chunk of space to make a so called "food forest" where you have a mix of species of fruit trees and shrubs.
Geoff Lawton is a great resource!
Not specific, but this site is a good starting point when looking for (generally) more ethical services. Many of the listed are open source, or were created specifically to combat these data sucking abusive monopolies.
https://european-alternatives.eu/