Ok, so if I get an external HD, and I install Ubuntu regularly on that drive,
letting Ubuntu use the whole thing, then I would just have to make sure the BIOS
knows to check for the external drive to boot from first, right?

I planned on using Wubi because I can get the latest release and updates that
way online, rather than an old CD or DVD with an older version or minus all the
updates.

Is there another way to download Ubuntu? Say, from a website to a DVD, then
install from there to the external drive? And then before I delete my Ubuntu
installation of the existing HD, from there I copy /home to another DVD and then
load it onto my external drive? Or just make a copy of /home and tell Ubuntu to
write it to the external drive?

Does that sound like a plan?