I've modded a couple of small games and I know that I'm happiest with groups of around 10-15 players and I absolutely can't handle more than 20. To some people, that would be a tiny, boring game, but I really like that musebox atmosphere. I don't think there's any perfect number for a player cap, but mods should recognize when their modding style or the game's premise is just incompatible with a large cast.