This guide cover almost all you need.
Personally i made a fresh Scale install, then upload my Core config file, and only some minor adjustment were need (like some change on command on cronjobs).
What can be usefull too Is a read on latest posts on this thread, just to be sure to not get pool exported (and panic).
What Is making me actually struggling Is the setting of the administrator user (root user should be disable, but when a core config Is uploaded the default truenas_admin getting deleted).
Did you already plan the jail migration? This Is the hard party