The game must be profitable for all parts. Don't forget ads
I'm not sure that people will pay 5-20 dollars monthly to earn maybe 3 dollars profit in the end playing every day. I think a f2p test could be nice to see if people will join, and you will have some feedbacks. If the idea and game are good the premium p2p options come next.
Upgrades ideas are nice, but it can't be so exaggerated or your project crashes.