Sorry for the long reply, such a great review
We are thinking in infinite mode to add bosses repeatedly, but it makes more sense for the story that they will still be once. For more variety I think it would be better to add more new regular enemies, but we don't plan to do that right now
Character upgrades are also planned, namely we planned that each boss will give us some kind of upgrade, but we didn't have time for that, so we limited ourselves to a large amount of gold.
Glad you like the project! :3