APFS questions

My sister just bought a 2013 refurbished 15" MacBook Pro (don't know if it is an Early or Late 2013). I don't know which Mac OS is installed but if she wants Mac OS High Sierra, will it convert the internal storage to APFS during the installation process? I'll be going down to her house either at the end of this week or on Thanksgiving to help her with files migration and setting up her email.

What will happen during the migration from her old 2009 MBP with HFS+ format internal storage, will her files be corrupted since they are currently saved to a non-APFS drive?

Will we have to convert all her external storage to APFS if the new MBP has High Sierra installed?