However, we've worked hard on the model and I think it should be somewhat different than the standard. We wanted a model that balances the reality of running a business with a system that is actually part of the game.
There is nothing you have to buy to beat this game.
We modeled it after an old-school arcade game. You have lives and spend them to revive dead characters. You can earn lots of lives through gameplay. If you completely run out, we treat it like a rogue-like. You can start over and get more lives free of charge. In the olden days the screen would have said "insert coin to continue." If you prefer, of course, you can also buy more lives.
So, a talented player can beat this game, earn upgrades, unlock new relics, etc. without spending money. If you want to play a lot of different characters and be a little less concerned about when or how often you die, then that's where the premium currency comes in.