After spending some time wireframing my ideas, I want to start building my rails app. However, I'm well aware that later down the line I'd like to consider multiple user accounts.

Should I be thinking about the implementation of this from this early stage, or is this something I can implement without too much fuss later?

It seems like something that would be stupid to attempt later, but part of me just wants to get the guts of the thing working - a couple of simply forms and writing/reading some stuff from the db.