I wish I could help you with the APFS, even though I do use it. I know you really only see improvements on SSDs, and I have the original hard drive that came with my MacBook. I plan on getting an SSD at some point, though. I did, however, look it up and there were a few websites saying that they saw improvements on both more free space and faster boot times. So that would be enough for me to believe that it works. I also went to the
@dosdude1 macOS High Sierra Patcher website, and he even says that "If you decide to use APFS, a custom booting method will be installed by the post-install tool, as the firmware of these unsupported machines does not natively support booting from APFS volumes. It is not quite as clean as native booting, but will not cause any issues while running High Sierra." So what I get from this is that there is no way (at least at the moment) to get rid of the black screen with text on boot up.