ESTALLIDOS includes experts in observational astrophysics, numerical simulations, theoretical modeling, and instrumentation. Working together on "star formation" for more than 20 years, we have played a leading role in the development of the field (> 1000 papers, > 30 PhD Theses). Our strength lies in the complementarity among the different expertise and in having intertwined objectives. In ESTALLIDOS 8, we propose to follow up on a number of previous works and then address several new challenges. The > 50 specific objectives have been chosen to be timely, to fit in well our expertise, and to represent the forefront of the field. We will upgrade our population synthesis models and empirical stellar libraries, complete ongoing surveys, and apply both of them to measure metallicities and other physical parameters in extreme star-forming objects (extremely metal poor, extreme emission, overdense regions, AGNs, metal-free stars, etc.). In addition, we propose to find and characterize the sources responsible for the (single or double) reionization of the Universe, to measure the intra-cluster light and the elusive cosmic-web gas whose infall maintains star formation, to find tracers of intermediatemass black holes, and to constrain the nature of dark matter. Among the challenges, we plan to use a number of brand-new facilities (JWST, WEAVE, MEGARA, etc.), to incorporate artificial intelligence (AI) aided tools in our analyses and, above all, to take up a leading responsibility in the construction of forefront instrumentation (TARSIS, MOSAIC). We can address this huge effort thanks to the existing workforce (> 45 researchers), our knowhow in the field, and a consolidated coordination structure.