By all means, please do keep taking a percentage as a sensible funding model; it doesn't seem at all unreasonable, and it ensures you'll stick around. I'd be more concerned if you didn't have any obvious revenue stream.
Alternatively, if you do make your site open (and that'd be awesome, please do), you should prominently encourage people to post tips to your repository.
I am glad you have thought about it it to this extent. It is always reassuring to see that the relevant point have been thought of, and that there is at least a provisional plan to deal with them. This gives me a fair amount more confidence in what you are doing.