Question: how long did it take to boot up the ROM after installing the boot.img with the Deathly Kernel? I followed your instructions and its been on the boot animation for about 5 minutes now.In twrp go to wipe then advanced, then select the data partition and choose "repair or change file system." This will give you the option to change to F2fs. Note that this will delete all the files on your internal storage.
In the lineage thread the unofficial Exynos 5420 builds use the latest deathly for each build, so I simply download their latest and extract the boot.img from the zip file. You can then flash that using twrp img flash to boot, then you'll notice if you install deathly Adiutor (last build from apkpure) there is a lot more options. There's really no other way to get it unless you compile it yourself from github.
On this thread they talk about how most ROMS prefer ext4 in system for stability reasons. As for cache, I haven't heard of anyone using it there so I didn't bother. And I know most modern phones use f2fs on data partition as default now. Also, as I said above, keep in mind this will delete all files on your internal storage.