Most of the support you end up doing for free is caused by a handover that ended at “here are your logins”. A slightly longer handover buys back the next six months.
The five things to send
Logins through a password manager share rather than email. A plain-language one-pager covering the three things they will actually change. A short screen recording. A written note of who owns updates, backups and hosting. And the invoice.
What not to send
Do not send a thirty-page PDF manual. Nobody reads it, and writing it takes longer than answering the two questions it was meant to prevent.
Setting the boundary
Say in writing what is included after launch and what is billable. Doing this at handover rather than at the first awkward request keeps the relationship intact.