Box 3, haha, you are dutchNothing, but if you are young, your only income is from trading, lots of daily trades ... I wonder if that would fit with Box 3.
You are right on with the primary or sole income source.. Everything can change now though with the new 'Kabinet', though I bespoke with my accountant who lol about the fact BD could facilitate that change in tax within 2y. But who knows? 