Just a small clarification: You are still "selbständig" (self-employed) if you do a "Gewerbe". The thing you don't get easily is a so called "Freiberuf", particularly if you don't have an engineering degree (though I managed to get it).
Tax wise it is actually almost easier to do non-EU business than doing business in Europe, because there are no VAT issues involved (and there are no tariffs on those things). You just invoice the net value.