Economic Nonsense: 1. Self-sufficiency and buying locally are beneficial

No, the reverse is true.  Depending on others for some of our needs and having access to goods from distant markets are beneficial, whereas self-sufficiency and localism usually leave people poorer.  When we buy things from others we have access to their skills and specializations, skills that can make goods better and cheaper than we could make ourselves. Households that make their own clothes and pottery are poorer than those that can buy cheaper, mass-produced goods.  It takes them more time and more resources than it takes producers who specialize.  The same is true on a larger scale for communities and nations.  Buying from others and buying from outsiders leaves people richer.

People who can buy from distant sellers can buy more cheaply, and are richer by the money they save.  Requiring people to buy locally often means making them pay more than they would otherwise need to, leaving them less money to spend on other things.

When governments of developing countries impose tariffs and quotas on imported goods in the name of "protecting infant industries" they are making their citizens pay more than they need to.  A prohibitive tariff on imported US tractors, for example, means that farmers have to pay more for locally-produced ones, making their produce more expensive.  The protected local tractor makers benefit, of course, but it is at the expense of local buyers.  The process opens up opportunities for corruption and cronyism as local producers lobby, and occasionally bribe, ministers to impose such "protection."

Wealth is created by trade and exchange, and is increased when they are increased.  Self-sufficiency and buying locally both introduce restraints on trade and exchange and lead to people being poorer than they need to be.  They are not beneficial.