The considerable attention paid to metal halide perovskites (MHP) in recent years led to several scientific and technological advances. This in turn raised important questions that currently challenge the limits of available theoretical techniques and atomistic models. At present, perovskite materials are mixed with each other in complex alloys and heterostructures, including 2D/3D compositions, combined with additives or protecting layers to improve their stability and/or defectiveness as well as assembled with carrier selective layers, other materials and components to turn them into devices. Considering the target applications, ambient conditions predominate with additional issues related, for example, to the intrinsic dynamics in action in the MHP structure that may not be well captured using static averaged structures. Based on a set of customized examples, this talk will summarize recent theoretical results obtained by our group that aimed at answering questions such as: i) How do these engineering strategies impact the work function and absolute valence band energy of the MHP material? ii) Is it correlated with surface/interface dipoles? iii) Can one quantitatively assess energy level alignments of MHP semiconductors based on first-principles electronic structure calculations? How can one get rid of the stochastic dynamics of organic cations and further include cation and anion alloying while computing materials properties? iv) Is it possible to extract semi-empirical formula for molecular passivation at surface or transitivity rules for interface dipoles? Special attention will be paid on newly discovered phases and compositions and opportunities to further engineer MHP properties in connection with their use in devices under working conditions. *This research received funding from the European Union’s Horizon 2020 program, through and Innovation Action under the grant agreement No. 861985 (PeroCUBE). J.E. acknowledges the Institut Universitaire de France.