I like the way you have listed the ways to earn extra income and was quite surprise that you did not make mention of network marketing, which is a way to make extra income without quitting your regular, though most people view mlm as a pyramid scheme but the real pyramid scheme is a regular 9 to 5, because you can only have one president of a company at any given time and network marketing business model to promote product that can be used is really cheap to join and can offer a substantial extra income or what do you think?
It’s my only property. I”m living in an SF rental and biding my time for a correction to buy again (maybe). One other thing I do like about the house is that there is dry powder in it that I’m paying zero interest on and can pull out to buy another house. I don’t know a lot of other ways to achieve that. I don’t have a traditional job, so the house is my only source of loans currently which I’ve been using to fund my 4-yo company.

Residual income is calculated as net income less a charge for the cost of capital. The charge is known as the equity charge and is calculated as the value of equity capital multiplied by the cost of equity or the required rate of return on equity. Given the opportunity cost of equity, a company can have positive net income but negative residual income.