Embedding theories offer an elegant solution to overcome intrinsic algorithmic scaling and accuracy limitations of simulation methods. These theories also promise to achieve the accuracy of high-level electronic structure techniques at near the computational cost of much less accurate levels of theory by exploiting positive traits of multiple methods. Of crucial importance to fulfilling this promise is the ability to combine diverse theories in an embedding simulation. However, these methods may utilize different basis set and electron–ion potential representations. In this first part of a two-part account of implementing potential functional embedding theory (PFET) at a correlated wave function level, we discuss remedies to basis set and electron–ion potential discrepancies and assess the performance of the PFET scheme with mixed basis sets.