Finding the kernel is not as easy as it used to be. You need to read the partition table on the disk. You need to be able to understand the filesystem that the kernel is stored on. This adds a fair bit of complexity.
On a modern UEFI system you actually get provided with an API that can do all that for you, though only FAT32 partitions are supported for the FS out of the box (you can load your own drivers for more).
If your boot partition is FAT32, UEFI makes things much much simpler.
True. And I think that's more than adequate for your homebrew OS. (Which can just have a second stage if you really need to boot off of an encrypted RAID-5 partition connected to a custom storage controller.)
Finding the kernel is not as easy as it used to be. You need to read the partition table on the disk. You need to be able to understand the filesystem that the kernel is stored on. This adds a fair bit of complexity.