So I got done the first 8 levels for my Sha Cat Lady. Feels Good.
Here some Screenshots of the two Level select Screens, each containing 4 levels
which have to get progressively unlocked by winning levels. 

The Plan
Until level 8 the game is totally free. In level 8 you arrive on a golden door, blocking your way.
You need the golden key for it, which you only can get by buying it, for around 1.99 Euro.
That’s basically buying the game or upgrading to premium. This will be the only time the player will experience a flow blocker in my game. But somehow I need to make money too.
I like food.