Thank for this extensive work. When you make extra money you need to think simple. First thing you should consider is whatever you do must be safe enough that you don’t lose your initial investment as well. Also, look at the ways you can reduce your costs. This could be car insurance savings or paying back expensive loans or card balances. Saving is making money as well.
For a person working for a wage, their source of income is their job, or their labor (aka their time that they sell to someone). But you can own a house, and rent it out, and when your renters pay you renter every month, the source of that income check is your rental property, or your house. It would just be called rental income. If you have money in the bank in an account that pays interest, those interest payments are another source of income. We can say the source is interest payments, or we can identify the asset that is generating rent, and say your money in the bank that is generating “rent” (aka interest) is your source of income.