Thanks jazzbiker.
Re. starting LBA - since it's working with "256" I'll continue to use that, though that will eventually be either a command-line option or a config file option. Or both, I suppose, with command line option taking precedence over config file.
Re. vfat - Since I was mainly curious about the EFI partition format because of a nagging (and possibly unfounded) lack of confidence in all things FAT, and since it seems to be working just fine for this purpose, I'll just continue using vfat for the EFI partition.
I'll confess that the graphical wrapper is the most likely to fall by the wayside if life gets interesting, though it doesn't seem like there's much risk of that.
@ CNK and Polikuo - Thanks to you guys, as well.
Without having looked into either method in any detail, I like the -idea- of command line options for GNU Parted better than the -idea- of driving an interactive program with a pipe.
But, if I decide to use the pipe strategy to drive gdisk then I'll likely do the same with fdisk to keep it symetrical.
Nothing wrong with using GPT, though I would expect to use the multiboot install primarily on USB sticks rather than HDDs or SSDs and I would not expect to see a USB stick over 2 TB nor needing more than 4 partitions. This, of course, from a forward-looking guy who once said, "I'll just get the 32 bit version of Win7 Pro since the machine only has 4 GB of RAM anyway..." (Still using that box 13 years later, wishing it would do any good to add more ram... though it might actually be time to retire it anyway, if only because the fan is loud.)
Of course I initially forgot to
sudo rebuidfstab - I was so frustrated after trying for several hours to build everything on "
/dec/sdc" that I'm lucky that's the only thing I forgot!