I got it to work... I must have done something incorrect when I installed grub the first time. After much internet searching, I found someone who had done something similar and I partially followed their instructions [https://gist.github.com/umpirsky/6ee1f870e759815333c8].
A quick update: I've reinstalled Elementary OS, and made it a bit farther. This time I did the following:
booted into the live ISO,
installed mdadm and assembled the raid where root will reside,
successfully ran the installer from commandline: ubiquity -b (using the -b switch runs the installer, but will not install the bootloader, which is where I was ...
209MB for a /boot partition is a little tight. This could make it rather difficult to install kernel updates. Some people are able to get by with a small /boot, though I tend to keep mine at 1GB in size. This allows for a good deal of breathing room so long as you can afford to forfeit the storage space.
As for your second question, it's not a terrible idea ...