Can't format drive to APFS on older machine prior to 10.13 install I have a Mid-2012 15" MacBook Pro that I've just put a new SSD into. 

I didn't format the SSD prior to putting it into the computer, my plan was to boot into "recovery mode" (not sure of Apple's term for it) by using command+R and running disk utility from there. 

I want to load High Sierra onto the SSD, which I would install via creating a USB installer. 

I understand that High Sierra runs best on APFS, but Disk Utility in recovery mode doesn't give me that option. 

If I go ahead and install from the USB, will part of the install process format the SSD to APFS, or do I need to format the SSD to APFS prior using another machine capable of formatting drives to APFS?
If you create a High Sierra USB installer, then you should be able to use the Disk Utility application to format the SSD as APFS before installing macOS.

If you boot from Internet Recovery using the Option-⌘-R keys then you should get the Mojave Disk Utility application. This can also be used to APFS format the SSD. Note: You have to have had macOS Sierra 10.12.4 or later installed before being able to use the Option-⌘-R keys.