Hey Dark,
For the game crashing, it'll probably depend on the specs of your Android device. I'm able to play through the game fine with mines.
For Junes, it will say you've finished all your shifts (after your third shift) and it will reset after the next in-game week.
Raising your stats will lead to more discounts depending on your rank (Bronze, Silver, Gold) and there are stat multipliers on the roof
The max is 4 since I haven't completed the game, next update will be 1.0 aka complete game.
There will be no paid version (unless you're talking about cheat menu patch) there will be early access then released to the public!