> But I have no idea what the migration of a decade of email across 5 inboxes will look like; not to mention Calendar and contacts.
Contacts and Email seems to be the easy part: you can download the emails via IMAP to a client like Thunderbird, and the re-upload them on a new account. Years ago I did this transferring from one G Suite account to another for a friend, worked very well. Contacts can be exported in CSV and then imported bia CSV, no big deal too. I have routinely transferred loads of contacts between different systems this way, including Gmail. With calendar, I never had a necessity to transfer data, but I imagine that there are ways, given that it uses a standard iCalendar format.
Are you sure about the re-uploading part? I've had an issue like that last week, and am currently stuck with my mails locally, not able to 'put them back' to the IMAP server. Not Gmail though.
I most definitely did re-upload it without any issues to another G suite account. It was in 2014 though, maybe something did change since then. Here [1] people write that there are probably some differences between Gsuite and regular gmail accounts.
Contacts and Email seems to be the easy part: you can download the emails via IMAP to a client like Thunderbird, and the re-upload them on a new account. Years ago I did this transferring from one G Suite account to another for a friend, worked very well. Contacts can be exported in CSV and then imported bia CSV, no big deal too. I have routinely transferred loads of contacts between different systems this way, including Gmail. With calendar, I never had a necessity to transfer data, but I imagine that there are ways, given that it uses a standard iCalendar format.