First of all, I know that Windows and Linux have some readability
issues, but I was wondering if it matters when it comes to actual file
type. That is, if I were to save a file as .doc in Ubuntu, and sent it
to someone using Windows, could they read it? That's really the most
important one.

I relatively new to Ubuntu as well. I don't think this (above) is a problem but
if you want to send me a sample file, I'll try to open/read it with windows.