MAORY is the ELT-MCAO system providing first-light wide-field correction for the near infrared imager and spectrograph MICADO. This paper provides an overview of the systems engineering processes and tools implemented to MAORY project during preliminary design phase and it illustrates, with some practical examples, the role of MAORY technical budgets to derive requirements on subsystems. One of the critical activities in systems engineering is the requirements managing. In line with this, the MAORY team devotes a significant effort to this activity, which follows a well-established process. This involves the MAORY requirements break-down to subsystems level and from here down to subsystems procurements specifications. This paper also presents an overview of the MAORY Technical Budgets. One task of the System Engineering is to manage the technical budgets at system level combining the contributors at subsystems level to meet the overall requirements.