Checklist for MX records

Checklist for MX records

I am trying to configure business email and I have added 2 users/ custom email-ids

I came to the configure email delivery page and it says

Before you change the MX Records, complete the following checklist:

  1. I have created all the user accounts
  2. I have created all the generic group accounts
  3. I have added the required members to those accounts
Does it mean that I have to create all 10 users/ group acconts of my free account before I change MX records ? Or is it possible to add users/ group accounts after changing MX records too ?

What does the last point mean -  I have added the required members to those accounts - is this only pertaining to group accounts I suppose ?