Hi Brian and welcome to forum!
I am not exactly a Linux guy, but I will do my best to help you out.
You did a good job with kick.rom and rom.key. They both belong to ROMs folder.
Just to clarify, AmigaForever does not include AmigaOS 3.1.4 ZIP. They are two different software packages. But no worries, you're all set with the Amiga Forever.
You can either make an ISO out of your Amiga Forever DVD and then use the ISO according to the manual.
Or you can try this. Insert your AmigaForever DVD, run AmiKit launcher and press Configure button.
Then go to "CD & Hard drives" section and click "Add Directory or Archive" button and enter
Device name: CD0
Volume label: AmigaForever
Untick the "Bootable" option.
And click "Select Directory" button and point the path to the root of your inserted DVD.
Then, still in the "CD & Hard drives" section untick all 4 options below: "Add PC drives at startup", "Include removable drives", "Include network drives", "CDFS automount CD/DVD drives"
And press the "Start" button.
When AmiKit asks you for the source of AmigaOS files, press "AmigaForever" button and your DVD should be recognized.