I can't believe that this is something people talk about. I've had a group of people in my head for years, complete with the mindscape the reddit FAQ talks about. I just thought I was a little bit crazy; it's nice to see that there's a name for it.
I can't imagine having to deal with just one though. I started with four, which seemed like a good idea when I was eleven, and I found that distracting enough. Having only one sounds like being locked in a small room with only one companion -- I'd rather be in solitary. I kept creating more regardless, and I finally ended up with sixteen (many of those only half-formed, to be fair), before I figured out how to get them to talk amongst themselves and leave me alone. Most are still there (a few seem to have disappeared), I just stay out of that room.
My advice would be to avoid doing this at all, but if you do, create at least two, and give them a nice room (or set of rooms) to stay in with a defined exit. You'll thank me later.
I think you may be generalizing from one example here. We're quite happy with just the two of us.Any more would be too crowded for us. I imagine the optimum size depends on the personalities of those involved. I'm not sure I agree about suggesting people avoid this entirely, but I certainly would advise caution.
Thus spake Eliezer:
It seems that many here might have outlandish ideas for ways of improving our lives. For instance, a recent post advocated installing really bright lights as a way to boost alertness and productivity. We should not adopt such hacks into our dogma until we're pretty sure they work; however, one way of knowing whether a crazy idea works is to try implementing it, and you may have more ideas than you're planning to implement.
So: please post all such lifehack ideas! Even if you haven't tried them, even if they seem unlikely to work. Post them separately, unless some other way would be more appropriate. If you've tried some idea and it hasn't worked, it would be useful to post that too.