Put it this way, here is my explanation in simple terms : - ). So when you do backup, it mostly takes care of OS settings side and sk @G_W_Albrecht provided is an excellent reference to that.
Now, as far as migrate_server, that will simply transfer the rules, objects, vpn communities, pretty much anything from smart console and you do NOT need to reset SIC again. By the way, keep in mind that migrate _server will override existing license, but would NOT "erase" existing IP and hostname, so if you go that route, I would give it appropriate hostname beforehand and also you can assign it same IP address, because it would not be in production until everything is moved over and policy applied from the new server.
Makes sense?
Best,
Andy
Best,
Andy
"Have a great day and if its not, change it"