The design of tokamak core plasmas inherently spans a wide range of modeling fidelities, from back-of-the-envelope scaling estimates to computationally intensive first-principles simulations. This talk presents an overview to navigate this hierarchy, combining analytic scalings, reduced transport models, and integrated multi-physics simulations to iteratively refine plasma scenarios. Emphasis is placed on how these tools can be consistently coupled within an integrated modeling workflow to balance physical fidelity, interpretability, and computational cost.