I have to say, I find this a bit nonsensical. Null's income may come from donations to him personally but there's no way that those donations are unrelated to Kiwifarms. The only reason to give him money is because you like Kiwifarms and want it to continue to operate. This is also, as you say, why he doesn't want Kiwifarms to only be available through Tor. He may not be getting the money directly from revenue through Kiwifarms itself but it is his primary source of income.
Additionally, this brings up another question. Does Kiwifarms have a regular revenue stream that isn't recurring personal donations to Null? I know that Null operates an LLC. Does Null's LLC actually make any money outside of personal donations to him? Are the donations made to him or to the LLC? Is there any meaningful separation between LLC funds and Null's personal funds?