How do I properly offer a fair commission for a Twitch Stream?

[Gary Flanagan]

So, i'm preparing a potential long term twitch stream (depends on generated interest. If I can get 2 loyal viewers, I will be running with this) for Legend of the Five Rings and i'm wanting input on a fair mixed flat rate/percentage mixture deal. As this is going to be a risky venture, I was thinking of offering 50% of all monetary gains from the stream along with a flat rate so that they would not be losing too much on nights that the donations are sparse/non-existent. However, as my experience with map making is pretty much slapping together sets on Roll 20/screenshots over Discord, I have no clue as to what would be a fair flat rate to ensure compensation for time and materials/use of program licences. Any input on properly creating a fair and equitable offer would be appreciated.

Edit: I would need a City map and a castle map right away, as well as a series of battle maps in the future.