I'd have to learn about monitoring the app properly.
Depending on popularity might need to be migrated off Heroku, as it's only free for a pretty basic service and we'll run into performance issues quickly. It would be cheaper to get a VPS. So there are a few things to think about, though it might not be an issue at all for a while.
An interesting conversation to have.
Lump sum per project per year seems like a good starting point. Free to friends and non-profit orgs.