Systematic reviews cannot be performed alone. One investigator is not sufficient to reduce the risk of bias in the review process. Not only must there be multiple people on the team, those people should have domain specific expertise. The Cochrane Handbook says:
Cochrane Reviews should be undertaken by more than one person. In putting together a team, authors should consider the need for clinical and methodological expertise for the review, as well as the perspectives of stakeholders. Cochrane author teams are encouraged to seek and incorporate the views of users, including consumers, clinicians and those from varying regions and settings to develop protocols and reviews. Author teams for reviews relevant to particular settings (e.g. neglected tropical diseases) should involve contributors experienced in those settings.
-Cochrane Handbook for Systematic Reviews of Interventions version 6.5, 2024, section ii.2.1
While not all systematic reviews are Cochrane reviews, the Cochrane is recognized as an aspirational standard. Ideally, your team would consist of Subject Matter Experts, a Methodology Expert, and a Population Scientist/Statistician. Ensuring you have a knowledgable team will help your review achieve success.
The team leader is often (but not always) the PI of a systematic review. It is important to recognize at least one person on the team as the team leader, because this will help the team remain focused and keep the team's attention on deadlines. While the process of a systematic review looks very "step by step", in reality the steps will overlap and it is important for one team member to be aware of what progress has been made and what elements need attention.
The team leader frequently manages documents/spreadsheets integral to team functions in order to stay organized and ensure the team continues to adhere to the protocol.