See http://www.towergames.com/ for a working indie online strategy game model.
One turn per day seems a little slow to me. Couldn't you program a simple AI that would allow players to try the game on their own? Giving people a clear idea of what the game is like without making them sign up will probably improve interest in the game.
One idea to get several people online might be to have a specific day or time when you encourage people to be online at once.