How to move config from fpbx 12 (Ast 1.8) to new server (fpbx 13, Ast 11)?

It has been a while since I built a new server and before I take a wrong step I wanted to check out the procedure. This is what I would do unless corrected:

  1. Bring old server up to fpbx 13 in module admin -
    — do I need to update all modules?
  2. take a backup
    — what level of backup? I just want the asterisk database and I ran into problems in the past moving too much.
  3. restore backup to new server…?

I also have custom stuff in extensions_custom.conf. Can I drop that in place and expect it to work? Or do I need to be aware of changes from Asterisk 1.8 to 11?

Thanks for the help.