Hi @Yevgeny_Libov ,
Here is a good document on migrating a standalone HA pair to Panorama -> https://docs.paloaltonetworks.com/panorama/10-2/panorama-admin/manage-firewalls/transition-a-firewal....
There are some best practices that we can learn from it.
Here are a few things to consider:
The Beacon free course Managing Firewalls at Scale has some excellent guidance on the last bullet.