Rerolls are the only way your squad improves, so the question is never whether to spend them but where. Set your current state below and the planner returns the priority that moves your squad rating most.
Claim the free rerolls first: like the game, favourite it, join The LockerRoom group, then talk to Sendou in the lobby for ten rerolls. Redeem the working codes on the codes page for roughly forty more. Only then start spending, and spend on empty or sub-60 slots rather than on players you like.
FAQ
No, and no site has them — the developer has not published drop rates. This planner works from things that can be observed directly: which rarity band an OVR falls into, how scarce goalkeepers are, and how deep each category is.
Because goalkeepers are the scarcest position in the game at 15 cards out of 214, and unlike outfield players they cannot be covered by a card cycling into the slot from another position.
Once you have committed to a Chemistry category, largely yes. Official art shows matched players 14 to 17 points above their base rating, which is bigger than almost any single-card upgrade you would be trading it for.