No investment income is not self-employed income unless you are in the business of investing or advising others on investing.

Business investment expenditures that depend on income or production (especially national income or gross national product). An increase in national income triggers an increase in induced investment expenditures.

Yes the amount would be a taxable income amount after your return of investment amounts exceed your cost basis in the investment.

investment APEX :)

Of course, not all investments are tax exempt. Investment income is generated by either the income it produces during the ownership of the investment (e.g., interest, dividends, or rent) or the gain it produces when the investment is sold at an appreciated value.