Galactic research has entered a thrilling epoch. Our knowledge of Galactic stellar populations, until few years ago mostly confined to stars at the solar vicinity, is rapidly extending to large regions of the disc and bulge of our Galaxy. Large spectroscopic surveys are acquiring an unprecedented amount of data, with radial velocities and chemical composition for hundred thousands stars, from the innermost regions to the periphery of the Milky Way disc, up to ~ 15 kpc from the Galactic center. This unique, because unprecedented, cartography of our Galaxy will acquire all its potential with the publication of the data from Gaia, the European astrometric mission, which will deliver positions and proper motions for 1 billion objects, and radial velocities for about one tenth of them. Without waiting for the final catalogue of the mission (planned for ~ 2022), with the second release of the Gaia data, scheduled by early 2017, the astrometric solution for most the sky will be made public, together with radial velocities for some ten millions stars. In less than two years from now, we will thus be able to reconstruct the orbits of several millions stars in the Galaxy, to have detailed chemical abundances for some hundred thousands and ages for several thousands. The tremendous amount of data that the mission will deliver will need efficient tools for their analysis but also sophisticated models for their interpretation. We are interested to answer to some of the simplest but still unraveled questions of Galactic studies : What are the characteristics of the different Milky Way stellar populations? How were they shaped over time? What is the evolutionary link between them? Which of them is the result of in-situ star formation or rather the deposit of structures accreted over time? The uniqueness of our approach consists in aiming to address them by using different and complementary numerical methodologies, that we have been developing in the last years and that are usually used independently one of the others: test particle methods, orbits reconstruction, chemical evolution, N-body simulations. From test particle methods, where the motion of “test particles” is integrated in a gravitational potential made of a thin and a thick stellar disc, an optional classical bulge, a rotating stellar bar, and a dark matter halo, we expect to have information about the level of complexity of the Galaxy. Can we describe it today "simply" as a disc galaxy evolved secularly in the last 8-9 Gyr under the effect of stellar asymmetries, and its main resonances? Or rather does the comparison with data available with the first Gaia releases indicate some complexity that these simple models are not able to reproduce? The reconstruction of the orbits of some ten million stars should help to understand the origin of the complexity possibly not captured by test particle methods, by quantifying the level of discontinuity in the orbital properties of the different galactic stellar populations. Chemical evolution models will reinforce our understanding, by providing: age-chemistry-kinematics relations, identifying the different chemical patterns and their possible in-situ, ex-situ origin; the star formation history of the Galaxy, and the mass of stars locked in the different stellar populations. All these ingredients will provide the basis for setting the scene for new N-body simulations, that will fully implement dissipative processes and detailed chemical enrichment. With them we aim at reconstructing possible evolutionary paths for the Milky Way in the last 8-9 Gyr, describing the chemo-dynamical links between the inner disc, the bar, and the bulge, and exploring scenarios for the accretion history of the Galaxy. Each of these methodologies, separately, allows to reconstruct some pieces of the puzzle of the chemo-dynamical processes experienced by the Milky Way. All of them, together, should allow us to build a robust and coherent picture of its evolution.