The number of players was not one of the major problems, really. If there was any problems with the players, it was the inactivity of many of them. I mean, I had to PM quite a few people, quite a lot of times, and it was not fun. Even when I didn't have to PM them, it took them a long time to post.
Simplicity was actually a problem in mine: I was constantly having too little rules in my RTD, while having many situations where rules would have helped. For example, the combat was far too basic, especially for the humans (how much damage does an arrow do? How much damage does a bolt do?), and there was no skill system, which was also a problem for people trying to learn things because they'd get attribute increases instead, leading to a compounding problem of people with too high attributes. This lead to many situations where I constantly had to decide what was "fair" for the players for their rolls and actions (which is a BAD THING because I am incredibly indecisive most of the time). Though maybe if you go enough in the other direction you won't have my kinds of problems. Go for it.
Being overambitious was DEFINITELY a problem in mine. Restrain yourself. Don't bother keeping track of various locations, nations, etc that the players will likely never visit again. Some of my players will even remember that war I had between two nations... heh, what a gigantic waste of time.