CAUTION: EDU used to have unlimited storage. Personal Gmail does not. Currently, your EDU account has a limit based on the level your district is willing to pay. If you transfer EVERYTHING from your EDU account into a personal it may not fit within the limits of the space available unless you buy more storage. Google Workspace file types like Docs, Sheets, Slides, Forms, etc. now take up space and could contribute to your Drive storage total. In addition, non-Google file types (pdf, video, pictures, etc.) take up file space. Pictures taking up space can be mitigated by using G Photo. Videos taking up space can be mitigated by making them unlisted videos on YouTube. Then just try to not use PDF whenever possible and keeping files in a personal email is completely doable.
Error message when transferring ownership outside domain.