Multiple sources of income is fine, I applied with 2. If you are not applying in the UK you may want to add a note of what zero contract means. Online teachers with limited income have been approved, main thing is the 500K.
I applied at Taipei which is infamous for its' focus on income aside from the 500k. I had very limited online employment income at the time of application so added investment accounts to show additional income. i chose Taipei as It was same day approval when I got it and did not want leave anything to chance.