I’m less familiar with gitlab than github, but typically your contributors are not part of the project team. The team are the dedicated people that control project direction, very often just a single maintainer. Contributors don’t need this level of access to help the project further. Issues are open for any contributor.
Currently in this thread there are 6 participants. Once the project starts anyone may want to make contributions, however small. Do you want to request project access for each and every one of them? Do you want to have minor contributors in a team? Do you want the barrier to contribute be as high as joining a team first?
I think best-practice is to keep your team(s) small, and only add members that have shown to be dedicated contributors, who are invested in the project. Often ones that request to be team members themself.