Best way to set up family email accounts with custom domain

I want to purchase a custom domain for my family to use. Needing 10-15 inboxes for myself, wife, kids, and a couple of inboxes for things like bills, streaming services, etc.

After I purchase a domain from GoDaddy (or another service), what are my next steps? Where can I purchase inboxes for a fair price? I would need to set up the inboxes on each of our devices (respectively only that persons inbox, not everyone’s).