Which patches are you using to enable sf command for SPI? The mainline Allwinner A10 SPI driver does not work with sun8i. The only driver I've found to work is this older fork.
It's been awhile since I've used an official armbian image. IIRC besides kernel related files, it's just overlays, bootscripts, and dtbs. Also, a couple of armbian related files that need to be kept if you want the armbian OS scripts to work (armbian-config, etc).