The first two weeks.
WHAT TO ESTABLISH BEFORE ANYTHING
What they need: how many sites, mailboxes, expected traffic
Whether a migration is involved Who owns their domain and where it is registered What they expect from you
THE ACCOUNT
Create it with the correct package Set a strong password and send it securely Confirm the domain points correctly Run AutoSSL Configure their mailboxes
WHAT TO SEND THEM
Their login details, securely How to reach support, and when What is included and what is not Who is responsible for backups Their nameservers
THE DOCUMENT THAT PREVENTS DISPUTES
A short written statement of what you provide, what it costs, what is extra, and how to contact you.
Two paragraphs, sent at the start, prevents most later argument.
DOMAIN OWNERSHIP
Establish now, in writing, that their domain is registered in their name.
Never register a client's domain in your own.
FOLLOWING UP
Check in after two weeks. Problems surface then, and catching them early sets the tone.